We currently have an IBM DS4300 Dual Controller Fibre SAN. It is a good box, but getting pretty old. It came with 256MB of cache per controller.
Recently we replaced the batteries in one of the controllers and noticed that the cache is a DDR PC2100 ECC DIMM. Of course, we are thinking about how cheap this RAM is now and is there any good reason we can't upgrade the RAM.
IBM used to have a "Turbo" upgrade to this box that doubled the cache and had a bunch of software features for about 10K USD. Since that product has been end-of-lifed, I don't think we can get that upgrade and we don't need the software upgrades (FlashCopy, StorageCopy, etc).
Besides the obvious potential warranty issue, what if any issues would we expect to see if attempting to put 2 - 1GB DIMMS in this unit?
Any other things I am missing here?

EDIT: Memory label:

Samsung  
CN 0433  
PC2100U-25331-A1  
M381L3223ETM-CB0  
256MB DDR PC2100 CL2.5 ECC