Alas, that's the thing about a used machine. Like Forrest Gump, you never know what you'll get
You got one that has an upper seal leak which has escalated into a transmission problem. When the tub seal failed, it allowed water to permeate the transmission thru the agitator seal. The water caused the oil inside the transmission to be displaced, hence the signs on the floor. You are facing a new transmission, which includes the seal kit needed to stop the leak. Unfortunately, about $120 in special tools are required to do work on this machine, as you will see from other posts on the Atlantis washer. Up to you to decide if this is really the machine of your dreams.