[Christ]

Yep, plastic end tanks, if you can't find the leak, try to bend back the tabs, break the seals on the tanks with a razor knife, and reseal the end tanks, then hammer the tabs back in place. Be VERY CAREFUL that you don't break the tabs. Try heating them with a soldering torch before bending them, they're not very strong metal.

If you attempt to re-seal the end tanks, make sure that you're using a coolant-tolerant sealer, like Silicone, lay a thin bead, set the end tank on flush, and then clamp the end tank on tightly after it skins over, but before re-folding the tabs. Don't refold the tabs until it sets up completely, as you could disturb the sealant.

If it was tweaked when you got it, you may have to re-braze the tubes to the end tank mounting plate in a few places. Best bet is to pressure test it with water in it, and mark where the water is spraying out.

Get a pair of rubber pipe caps from a hardware store, punch a hole in one and bolt in a clamp-type valve stem. Clamp them both on, fill the rad with water, cover the discharge port for overflow, if equipped, set an air regulator to 16-20 PSI, and pump it up and maintain pressure for a few mins. If no leaks, no problems. If it's leaking, mark the location prior to evacuating the water, then disassemble and seal leak.