I have some old firestone pin locks that I have been rebuilding lately. One of the kegs appears to almost be leaching out rubber. I cleaned it pretty thoroughly, and a few weeks later after handling it, I found that it was leaving black dirt on my hands (the kegs were not stored in a dusty room). Is it possible that the rubber is leaching out of the keg's handle / bottom? If so, should I not use this keg or is there a way to keep the rubber from rubbing off like this?