If it is a new seal, you should be able to use a 2x4 and a mallet to just go around the outer edges of the seal and tap them in. Also, since you didn't use the regular fill hole, you may have just overfilled the transmission, and the seal is leaking because the oil level is just to high.
Matt: All I'm trying to say is that the motor should start, irrespective of if the clutch is hooked up or adjusted properly, or not. The switch that Honda uses, on a manual transmission is activated by the clutch pedal, independent of the clutch cable adjustment. You would still have to get the clutch adjusted properly to drive, of course.
But if his car is in 5th or something and in gear the engine won't be able to start up because it well be trying to move the wheels as well, correct? I've accidently done it in reverse and it jumped, but I don't think it would have enough torque in fifth to get it going.
If I understand correctly, he has an 89, previously with a DX transmission, swapped to an HX. If that is the case, then YES, it very definitely uses the clutch switch. (I was under the dash on mine a couple of days ago, working on my Codfishing outfit).
Ok, so what your saying is he might have it in gear? You could be right, but if he put's it into neutral, then it shouldn't matter. ( I'ts interesting the things I take for granted because I would have put it into neutral, automatically).