If you still have them, try lightly brushing the contacts with a pencil eraser until they get noticeably shinier and then rub them off with a paper towel.
Lots of old memory modules stop working or get memory errors due to the copper contacts getting tarnished, I have this problem all the time with my memory stash. Though I use a non-abrasive corrosion inhibitor to reduce wear on the contacts instead, but a pencil eraser once or twice won't do much harm.
I'll give it a try, thanks!