I did the clutch in my brother's L series about six weeks ago, it took me (working by myself

) just over 2 hours in the driveway with limited tools (mine were at work).
Easiest way to do the clutch is to rip out the motor. To do that you disconnect all hoses and cables between the body and the motor, drop the exhaust, undo the two bolts under the engine mounts and the bolts and nuts between the engine and gearbox. Old clutch off, new one on and as visually central as you can. Don't tighten up the clutch bolts completely, do them finger tight. This way you can line up the clutch with the input shaft quite easily, then tighten up the clutch bolts through the starter motor hole. Easy peasy.
As for the oil leak how much has it dropped? Like Mike said, its probably the rocker cover gasket. Personally I replace these in pairs, up to you if you want to do the same. Definitely heaps easier to do with the donk out.