Or isopropyl alcohol. Remove the old battery first.
You will have to clean into each pin socket to get good metal to metal contact on the CPU legs. That might be the basis of your problem.
Also the Mega Chips have been known to crack your on board Agnus(Not Agnus that's the one in Franko's Amigas) socket if they aren't treated carefully. Check out the Agnus socket in the corners and make sure it isn't cracked. If you have an Agnus chip remover I would try the chip in the original socket once you get the CPU socket cleaned.
Good luck.
