I'd yank that silly IBM ATOnce clone thing but quick. Probably the point of contention in the system too. Yes, yank the 68000 off of that and reinstall directly into the CPU socket. Be careful to observe correct notch orientation.
Best way to clean IC pins is to simply remove and re-insert them. The friction of the sockets is usually enough to "clean" 'em. If they're truly oxidized, get yourself some very light grit sandpaper or a fiberglass brush to clean 'em up.
I'd be willing to be though most all of your problems will be solved once you get that AtOnce board out. All the chips, but especially the Kickstart, CPU and Agnus chips all deserve to be re-seated.
