camshaft seal

Bought my first Mercedes a couple of months ago, '89 300SE and I love this car! It ran great up until a few days ago so I thought I would replace fuel filter, plugs, wires, cap and rotor. All went well until I removed the distributor cap and it was covered in oil, so much that I'm not sure how it ran, the cam seal is obviously leaking, and not being familiar with these engines I'm wondering how much of a job it is to replace. The car is a daily driver so I can't have it tied up for too long. Any help would be appreciated, thanks:
Eric