In total agreement here. Erasers will damage the gold contacts but alcohol (or contact cleaner) won't, unless you dunk the camera/lens in a bucket of it.
camerapapi wrote:
"Never, never use a pencil eraser on the gold contacts. The gold on the contacts is only a few molecules thick and you will wear it off quickly. Gold does not tarnish but it can get dirty. Wipe them off with some alcohol on a cloth. They do make contact cleaner but alcohol does the job"
I am 100% in agreement with this. I use a contact cleaner made by TMC.