Buying "chain store" reman electrics is a crapshoot - they offer a lifetime warranty, but you'll NEED it.
It's possible for oil to get into a starter motor and cause trouble - I'd fix the oil leak first. Use a gasket, and use LocTite 518 "Gasket Eliminator" to seal it.
Here's the catch...
1) Install about four studs meant for SBChevvy "Cast" valve covers into holes in the head for the valve cover bolts. Make them more or less even - this will help you later...
2) Coat both sides of the gasket with #518 and set it in place on the cover. Go work on your beer (or beverage of choice) for about 10 minutes to let it tack up.
3) Pick up the valve cover, and set it on the studs. The studs will help locate the thing, so you don't have to wrestle with it - and keep the gasket from shifting.
4) Install all the bolts FINGER TIGHT ONLY, and put studs on the nuts FINGER TIGHT ONLY. The underside of the bolt head/nut should be making contact with the metal valve cover - that's about IT.
5) Go have lunch. Take at least an hour. #518 is anaerobic and has a LONG work time when exposed, but this is shortened once it's exposed to air and cut off again. This will allow it to start really setting up.
6) Come back. Grab your "little" torque wrench, and tighten the bolts to NOT MORE THAN 84 pound-inches/7 pound-feet. I did say "little" wrench - that's what you want. If you don't have one, go get one - you'll also need it if you ever do the oil sump gasket (which torques to either 84 pound-inches or 132 pound-inches.)
7) Allow to sit for at least four hours - prefereably overnight. Start it in the morning.
I've done this three times so far (three different XJ's out of four) and haven't had a bit of trouble afterwards. This WORKS.
5-90