This is a pretty basic procedure and very doable DIY job -- even if you haven't done any work underneath your hood yet. The beauty of the 103 engine is how easy it is to work on.
- gasket sealant part #002 989 45 20 10 (about $17 per tube
- new "U gasket"
- new camshaft radial seal
- new valve cover gasket (might as well, while "you're there")
1. remove valve cover (10mm bolts, 10 or 12 of 'em)
2. remove fan shroud
3. remove the distributor cover, and distributor cap <--- 5mm hex
wrench -- 4 bolts (long wrench here helps on one of the bolts)
followed by the distributor rotor -- 3 small hex bolts hold it on
2mm? I think. Careful not to strip these.
4. remove the distributor driver -- small metal T shaped piece that
is held on by a torx bolt --- forget size... want to say 6
5. unscrew coolant resevoir cap and remove the water return
pipe --- you may want to buy a new rubber o-ring that attaches
on one side (metal into metal side) ... in fact this is a no brainer
since they're only a buck or so.
6. unscrew the 4, 13mm bolts that hold the front cover on and
bang it off carefully with a rubber mallet or something similar
7. remove old U gasket and clean all contact surface of old sealant
with gasoline or other mineral spirit.
8. replace radial seal on cover if it's leaking -- otherwise I'd leave
it. It is pretty easy to press out, and press new one in.
9. place a dab of sealant in very corner where each end of the U
gasket makes contact, and put new U gasket in place
10. coat edges (where front cover makes contact) with sealant --
I use my fingers. You have approx 15 mins before the sealant
11. put front cover back on -- this part is tricky because you don't
want to fold over the U gasket, while getting it in place just
right. The manual says to use an insertion sleeve to help it on
but I've always done OK without it.
12. tighten 2 bottom bolts first -- torque is 21 nm
13. love this phrase -- replacement is the reverse of removal....
replacing the valve cover gasket while you're at it.
I may be missing a step or two, it's been so long since I've done this... but I'm pretty sure this covers it.
As Mike stated --- this is all documented in the 124 series MB repair CD, and if you plan on doing most of the little problems that, if they haven't popped up already from previous owner, will at your mileage -- then investing in this wealth of knowledge may be a good idea.