Of course the door to case could be the main leak, but you would need to remove it and look carefully at the mating surfaces (I would do this regardless if you have the primary stripped apart). Whilst the cover is off you can inspect the dowel pin and make sure it is secure (it is unlikely to be this pin but I have seen them loose) clean up all the bolts and threads (1/4 whitworth threads) check also the bolts as they are often stretched from folk over tightening them, if this is the case, then replace them all. I install the cover with a bead of Threebond sealant and I also smear some on the bolt threads before I install them all. This tends to stop the bolts coming undone, wire locking is ok, but I don't bother normally except the upper one at 1:00 o'clock that is wired to the detent plunger cap in front of it. Do check the G 24 seal, these can be overlooked often and they are easily damaged if the slots in the bearing retaining ring are butchered. Because of these slots there is little sealing purchase for the seal, so use a small amount of sealant to help the new seal go in, and press it in with a flat plate or socket to keep it square. Finally make sure all the surfaces and case threads are thoroughly clean before assembly.........Good luck with it all.......... Greg.