Quote:
didn't inspect the caps prior to use
Well, I think there you have your answer. Using an ECU without replacing the caps is like playing Russian Roulette. Its just a matter of time until things melt down. The second ECU, the one your friend said he had replaced the caps, I would write that one off as probably a victim of acid residue damage. Too many people only replace the caps, and don't take the time to clean up all the acid, and its inevitable that the ECU will eventually malfunction. The acid gets under all the components and continues to do its nasty work, even years after the caps have been replaced.
If you didn't flush the connector off well with some type of electrical cleaner, the green stuff is probably residue from one of the first ECU's. Either way, I would recommend you clean it well with a good contact cleaner to neutralize the acid.
Now you know why I only deal in 1994 ECU's. I won't touch ones with acid damage, except to remove parts from them and then throw their acid-eaten carcass in the trash! /ubbthreads/images/graemlins/devil.gif
My ECU's might cost a little more than one off eBay, but you are getting one that has NEVER had any acid leakage, and never will. That little peace of mind is priceless, IMHO.