All of this! I'd say if you could afford it, get all new gaskets and seals, they shouldn't be too expensive and the last thing you want really is to get it back together to find that a joint has failed somewhere and you need to re do all your hardwork. If its apart and you can get the spares just swap any and all seals you find. A bit of research online and you'll be able to find all the stuff you need. The first time I stripped an engine down I felt the same, but its not difficult when you get stuck into it. What makes it difficult is when something goes wrong (which is when you come back and ask more questions) or when you don't have enough room for your stubby little sausge fingers (Curse you genes!!) Oh and one more thing, before you start rebuilding make sure everything is given a damn good clean, especially sealing surfaces. A nice clean surface will mean a better seal and save time later. The point I was actually making was that with the exception of the clutch cover gasket there are no other oil tight gaskets to replace. This is of course if you leave the top end untouched. The crankcase is joined metal to metal with a jointing compound. Definitely replace oil seals though.