When trying to repair my massive oil leak on my 83 300D, I thought I had it narrowed down to a bad gasket on the vacuum pump. After I got in there, I found both plugs that are in the 7 and 8 o'clock position from the vacuum pump to be finger tight. This was the real cause of the leak.

My 80 240D has had a very slow leak from the engine front driver's side for several years...not a big deal. For kicks, I got in there and found the same two plugs loose on it also. I tightened them up and it seems that the slow leak is now gone.

So if you have an oil leak on the MB 123s coming from the front driver's side, check those plugs near the vacuum pump. You might find like I have that for some reason, they have gotten loose and are leaking motor oil.

thanks
Joe