I just replaced the lower pan gasket on my 83 300D. Not difficult at all. I used a very, very thin skim of silicone sealer on both sides.

Are you sure that it's the pan gasket that's leaking? I thought for for a long time that my 240D pan gasket was leaking but it turned out to be that the 2 plugs near the vacuum pump were loose. If the leak is towards the driver's side front of the engine, I would look there.

Joe