I have 2 old Line Material Industries 400w MV paint can style ballasts . Both have rotten insulation with bare wires showing on the outside. Besides , I'd also like to check and/or replace the caps if needed . I just don't want to damage either ballast trying to disassemble something that's not designed to be disassembled !!

 Any thoughts

Yeah, I'm not sure about the really old ballast cans. Some of them look like they were sealed like a tin can with crimped or soldered on lids. If you can't see any visible fasteners that might be how they were sealed up at the factory. Soldered might be the easier of the two to open up as you might be able to get it apart with some heat. The other thing to look out for is that some of the older ones might have been potted.

The newer Advance can ballasts I have look like they're a breeze to open up. On those I believe you can open them up if you unscrew all the screws holding the can on to the baseplate.

Do you have any pictures of them? 

The 1st one : https://www.lighting-gallery.net/gallery/displayimage.php?album=5203&pos=69&pid=159016 Definitely looks crimped . Them 2nd one I don't have a photo of yet , it looks to be both crimped and have what looks like some sort of rivets/pins in it. I'll try to post some photos this weekend  . 

Yeah the first one definitely looks crimped. I don't think they were intended to be opened up for servicing without some major prying. The cap is a issue but if it's just the wires, I would look into using some heat shrink over the wires. Maybe you could use some liquid electrical tape to build up the areas with missing insulation before protecting them with a overwrap of heat shrink. Then give the can a new paint job and it'll probably work if you use it occasionally. 

The 1st one : https://www.lighting-gallery.net/gallery/displayimage.php?album=5203&pos=69&pid=159016 Definitely looks crimped . Them 2nd one I don't have a photo of yet , it looks to be both crimped and have what looks like some sort of rivets/pins in it. I'll try to post some photos this weekend  .

Cut it open, these are sealed