98 taurus engine replacement

I just had a rebuilt engine put in. I drove it 1 day and the transmission started leaking severely. Took it back, they said was leaking between torque converter and transmision. They said they did not touch this area and its not their problem. It was not leaking when I took it to them. After driving for about 30 minutes and stopping it leaks about a cup of fluid. They said they just bolted onto torque converter.
Could they have caused this problem and what should I do?
Thanks

They could have caused the problem if they improperly removed and re-installed the tranny. I would hit them up for the repair. It's a cheap gasket, but the labor would kill you to fix, especially since you just had that part of the drivetrain apart, and paid a lot of money to do it. Considering what they profited on the engine swap, they should not have too much of a problem throwing a new seal in there for you. You should pay for the new seal and fluid since it those are wear items.