I have used the above procedure to replace the valve stem seals on two of my M103 cars. My '92 300e went from using 1 quart in 750 miles to less than 1 quart between changes (3000 miles). My '88 260e improved a little too but still uses about 1 quart in 1500 miles.

When I worked on my cars I brought the piston to TDC just as a precaution in case something went wrong so I wouldn't drop a valve into a cylinder. With the piston at TDC the valve only drops about 1/2" before hitting the piston.

I did it like this: When applying air to the cylinder I was working on, I rotated the crankshaft a little past TDC and put a ratchet and breaker bar on the cranshaft pully to keep the engine from turning. Going past TDC causes the crankshaft to turn clockwise against the ratchet (yes, this is the direction to loosen the crankshaft bolt but it is torqued on so tight you don't have to worry about that).

Also be very careful not to drop any of the little valve cups or keepers because it appears they could go down an oil drain hole and disappear into the engine. I tried to keep the drain holes covered with a small rag.