Rubber Degrading on Keg

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?

I have one that does that every time I wash it. I guess after a while those tops and bottoms just start to break down and get black stuff everywhere. Not sure what to do about it, but there isn't any worry that it will harm your beer, it' all on the outside, the stainless inside should be fine for a long long time.

I soaked the ends in a hot water and oxyclean mixture. Then I scrubbed them really well with a green scrubby pad. Then I armorall on them. It cuts down black rubbing off.