Which RAM chips is faulty? Not all? Replace just the broken one. You get the error code on screen wich shows the location of the fauwlty RAM?

I had one replaced on my //c about an year ago and i think i used one of these:

Vintage MICRON 4264P RAM MT4264-15 16-PIN DIP NOS

http://viewitem.eim.ebay.fi/Vintage-MICRON-4264P-RAM-MT426415-16PIN-DIP-NOS/370632681775/item