I've not done this yet, but probably will soon as the 300TE leaks too much.
Remove the distributor, rotor, and rotor carrier. You may have to use a puller to get the carrier off, even after you use penetrating oil on it after taking the bolt out.
Remove the heater water crossover pipe -- remember to get a new seal for it for re-installation. It's held in place by a bracket and the heater hose, I think.
Remove the four bolts and tap cover off with a soft hammer. It will be stuck since the head contact area has RTV sealant on it.
Clean it all up, toss the old seal, and clean the groove the seal goes in. This groove MUST be completely dry and clean, no oil, dirt, or sealant of any kind.
I'd replace the cam seal, too, it is probably bad, and will leak oil into the distributor eventually.
Place a small dot of the correct RTV sealant (black, I think, not orange) in the corners of the seal groove at the head, just enough to seal the ends in place. Install the seal right side up and press the ends into the sealant horizontally -- that is, put them into the groove and push rearwards, don't push them in from above.
Lay a narrow bead of RTV sealant on the head /front cover contact area, then put a very thin layer of grease on the bottom of the front cover where it's going to slide over the seal.
Start the cover onto the guide dowels, and push down on it so that it slides on square -- if you allow the guides apply the pressure, the seal will almost certainly roll! This is the hard part. Take a mirror and a light and check through the space between the top and bottom covers to make sure it is even all round and that the seal isn't rolled anywhere. If it is, pull cover and try again, it will leak if the seal isn't perfect.
Have a care not to cut the cam seal, too -- MB has a fancy tool, but I usually make do with removing any burr on the cam and liberal use of oil on the seal. Make sure the lip points inwards and isn't rolled over, too -- it can be coaxed around with a blunt scribe.
The really bad part about this repair is that it is only temporary -- the front cover will start leaking again in about 30,000 miles usually.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!