What does the corruption look like?
It's possible that it's an overheated U202/U203 PAL. This is a common problem for A3000s and is a cheap fix. Mine manifested itself as random dots that speckled the screen and got worse with disk activity and mouse movements. Others have reported horizontal lines, corrupted gadgets, etc.
Also, yes, the Amiga 3000 did come as 1M CHIP. My 030/25 came with 1M CHIP/1M FAST. I swapped the 1M FAST to CHIP and replaced it with 8M FAST with the first paycheck after I bought the thing.