Hopefully your issues are just the connectors and not another issue with the board or chips..
My experience--
I have a 8MB rack emaxII that had similar issues "memory size errors"
1) I pulled the mem expansion board and sprayed the connectors with non destructive contact cleaner.
2) Re-soldered verified the solder connections were good (First time only)
3) Did the same thing to the Main Board.
It worked great for a couple of months then worked it's way back to the same condition after about 1/2 year.
I followed the same steps as above (except soldering) and again it worked for a few months then had the same issue a few months later" Memory size error".
So far though the last time did one extra fix after cleaning it and now it's lasted for at least 2 years. My secret weapon was to place a fairly stiff adhesive backed foam below the motherboard to the chassis under the main board connectors (2 ea about 1/2" wide by 1/4" thick maybe 3"long)---i think. This raised the corner of the board up slightly. Then when I replaced the mem expansion board back on It felt like I had a better click for the connectors than I had in the past. Also when tightening down the screws for the expansion board the screws had pulled the board tight to close a gap of about 1/32".
I have a theory that the main board may have warped through time due to age and had a tendency to pull away occasionally. Especially after it has been removed and replaced a number of times. I think the foam is acting like a cushion to help keep the connectors together.
I hope this may help you solve the memory issue.
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