n1k head unit question?

sold blower to a guy and it was in perfect running order when i took it off. i even fired it up on the car before we took it off. now there was an oil stain on the bottom near the plug and the drain. not dripping wet, just a dirty oil stain. i adv that i had leakage from the drain hose a couple times and had to cut it and reclamp it, might be from that. also there was some oil on the oil inlet line on top that could have run around to the bottom of the case but no seal leakage. no oil in the discharge tube. guy is telling me it looks like there is a seal leaking in the back, on the bottom. the cad blowup of the head unit doesn't show a seal back there, just bolts to clock the blower. this unit is only 18mths old with about 4k on it. he wants to send it to paxton to check it.
what do you guys think.