Bob,
1) You've got 2 o-rings between the intermediate and upper housing. These are the main o-ring, P/N 925259 and the oil return pipe o-ring P/N 125017.
2) Drain plug o-ring P/N 955974 or gasket 804261. Depends which you have on yours.
3) On the upper end, 804261 is the gasket for the dipstick but some have an o-ring, P/N 955974. Again, you'll need to check yours. 897682 is the gasket for the fill plug just above the shift shoe but not all have that plug so you'll need to look. 955989 for the hollow bolt on the cover and 832669 is the main o-ring for the cover and has an extra little loop in it.
Some extra items:
a) The filler neck is a replacement item so it's a good idea to at least take the hose off and check it while you have the gearbox off.
b) I think it's a good idea to pressure test the drive before disassembly to get a heads up on any other leaks before you take things apart. That way, you'll know before hand and can order those o-rings ahead of time.
c) The bellows is a replacement item as well but I've heard different life expectancies. If over 2 years old, I'd replace it just to be safe.
d) It only takes a few seconds to check the clearance between the upper gearcase nut and bearing (page 42 of the manual). That'll tell you if there is wear on the brass washer on the bottom of the gearbox. This was the reason for removing the gearbox cover plate.
e) If you find water or oil in the bellows, you may have some other significant problems . like the gearbox forward washer (# 23 in the drawing and P/N 832675. It's o-ring (P/N 956000) can get cut if there is rust on the washer or it could be the source of oil in the bellows. Of course, the presence of water in the bellows allways makes the PDS bearing suspect and you know what Rick will have to say about that!
f) You can use Permatex 3H aviation form-a-gasket as thread protector/anti-seize for bolts below the waterline and it's a good idea to coat the upper and intermediate mating surfaces with it as well.
That's all I can think of except perhaps covering up the intermediate housing studs with rubber hose to keep from scratching up the gearbox too much while putting it back on.
