Start with the lubro moly treatment. My 99 E300TD Responded very well to it.
There are two lines right rear side of the engine bay (feed and return). Disconect the two clamps and shove on two 12" hose extentoins with some copper tubing to join the existing hoses. Then an extra piece of hose to connect the two steel lines together. Use an old coffee can stick the two hose ends in the can. Crack open the LM pour it in the can . Start up the car and let it run
Follow the directions on the LM can.
See pics
-Anthony