My washer is leaving grease stains on dark clothes

My 8 year old dryer is dying. I don’t want to fork out the money for front loaders right now, so I am attempting to fix it. I just don’t know what "it" is. My washer leaves little to semi big grease stains on all colored clothing except jeans. It is most noticeable on dark shirts, mainly my own. It started rarely, but seem to be doing it more often. I was searching online, and one person said that it was the gearbox seal. Does anybody know? This is the only problem I have had with the set. I am willing to buy the part and fix it myself, just to save 3k for not having to buy another set. Please help me.