I have an old rapid start ballast, still works, runs one 40 watt lamp, it buzzes a bit but not a lot and seems to run about as hot as you would expect, hot but not too hot to touch... it is not currently leaking tar as far as I can tell but it had been in the past as it is running down the side and on the inside of the fixture... could it just have overheated because of a bad or wrong lamp and it still be safe to use, or if it overheated enough to leak in the past is it damaged and should not be used?

It had a general electric Ecolux lamp in it when i got it, ecolux makes it sound like it is some sort of energy saving lamp, but from what i can tell it seems to be a normal 40 watt tube. so i am not sure if that could have done it or not.

a ballast isn't necessarily bad if it shows signs of the insulating tar leaking, but it has absolutely seen some abuse. that is a clear sign of overheating, and i often find that dead ballasts have evidently leaked quite profusely, but i have also encountered numerous fixtures that worked fine despite a significant amount of evident leakage on the ballast and/or sheet metal below. i wouldn't say it's a good thing by any means but i still consider a ballast serviceable if it's leaked some but operates reliably. if it sees continued abuse it will most likely fail due to heat but if treated properly it'll probably last a reasonably long time.

It had a general electric Ecolux lamp in it when i got it, ecolux makes it sound like it is some sort of energy saving lamp, but from what i can tell it seems to be a normal 40 watt tube. so i am not sure if that could have done it or not.

i wasn't aware of any ge t12 tubes being branded "ecolux", i thought they just used it for t8s. they used the "watt-miser" branding for energy saving t12s on all the ones i've seen. if it's a normal 40-watt bulb i assume it's printed with "F40T12", then? if it says "F34T12" then it is indeed an energy saving tube... a lot of the earlier ones actually have "34w" or "34 watt" proudly printed on them but still call themselves "F40T12" as well.

... well, i did some quick research and it'd seem that they did indeed have a whole line of "ecolux"-branded t12s: https://products.gecurrent.com/sites/products.currentbyge.com/files/documents/document_file/81175_T12_Ecolux_Lamps_SellSheet.pdf i was rather surprised to note that document is dated as recently as 2013. without knowing what's printed on the bulb it's hard to say but it seems it certainly would have been possible to get an ecolux-branded f40 bulb, not that it'd be anywhere near comparable to a real f40 from before mercury content got so heavily restricted. it's certainly true that some magnetic ballasts really don't seem to like the 34-watt energy-saving tubes for one reason or another, i often notice they're more prone to striation  and the light has a sort of "dingy" cast to it. i'm not sure what the gas fill in those is but i suspect it has a lot to do with that. i'm not sure if that actually causes the ballast to run hotter but i wouldn't be surprised in the slightest... the kindest thing you can do for an old rapid-start magnetic ballast is give it proper bulbs from the same era when it was made. they'll run all sorts of things they weren't meant to (which really more or less means anything from the 21st century thus far) but they often aren't happy about it at all.

yeah, it says ecolux with starcoat (whatever the hell starcoat means), it looks like cool white to me, it just says f40t12 on it and nothing else about being 34 watts, so I am guessing that it is a normal f40t12 bulb, the phosphor is kind of uneven and it looks like crap. I put it in a preheat fixture and it will not do anything at all, so there is something weird going on with it. but i left the fixture on all yesterday and all night last night with a Phillips Alto f40t12 because that is all i could dig up and the ballast got warm but not hot, and it actually completely quit buzzing and is completely silent now. so i guess it should be okay. I will just have to keep an eye on it constantly because I am a bit paranoid. 

the ballast that is leaking does not say no PCB, should i assume that it has PCB? if so should i just leave the leaked tar inside the fixture and close it up, or should i try to clean it?

I don't want to sound like I'm shooting off my mouth but as an electrician if a ballast has leaked tar in the past it shouldn't be considered reliable anymore.
You may get some use out of it for a little while longer but you can't put off the inevitable forever.

As for the starcoat that you mentioned.
That was introduced by GE during the early- mid 90s for their T8 fluorescents.
Supposedly tubes with starcoat had better color rendering and more lumens.

yeah. i have 2 of the same exact fixture, the ballast in one is not leaking at all and the other is, they have the spot for a starter socket, so I am thinking I am just going to try to find a preheat ballast for it and put that in there, either way i payed $1 for the two fixtures, so it does not really matter. i just need to find a preheat ballast that does not cost an arm and a leg. as for the ecolux lamp with starcoat, it says it is an f40t12 and it says under it 40 watts. it seems to work fine in a rapid start fixture and I hate to get rid of a working lamp, so would it be okay to continue to use that lamp on a rapid start fixture? maybe put it in a cheap shoplight in the shed or something?

You should be just fine running the ecolux starcoat tube with a rapid start ballast, no problem there.
No reason to get rid of a working tube.
Besides if you're like me all you use is T12 anyway.
Yeah trying to find a preheat ballast is going to be difficult but even if you find one that is pricey if you can manage it I'd say grab it.
Let's face it, this kind of equipment isn't going to be around much longer so sometimes you have to step up to the plate and pay what they're asking.
This lighting hobby sure gets expensive real quick!
I've paid a lot to keep all of the T12s in my place working but it's worth it!

I am going to look for a preheat ballast, yes, all i use is t12 lamps. I do prefer preheat, but rapid start is fine with me as well, but if I am buying a ballast it is going to be preheat.

Ecolux tubes have reduced mercury content for TCLP compliance compared to non-Ecolux tubes.  Kind of GE's version of the Alto.

If its a leak Transformer it will be just fine.

You could try and re pot the ballast, some have tried that and that seems to work.

it is just a standard rapid start ballast, so i am not going to mess with re potting it. i will keep it because it works okay, but i am going to convert the fixture to pre heat.
I found a brand new in box advance pre heat ballast for $15. hopefully the capacitor does not blow up because it has never been used.