Engine/Transmission (1998.5 - 2002) Slave Cylinder Troubles

[JKaltenheuser]

A friend of mine has a 2001 6spd. He thinks the slave cylinder is bad, so he ordered one from Napa for the 12v because he heard it was better part # 360051, but when he put it together, the oil from the resivoir ran out onto the floor when he took the cap off. It leaked from between the line and the cylinder. Any ideas of how to fix this? He did place the new seal in the cylinder.