Timing Chain Cover
I too had a timing chain cover leak in my '88 260e with 130,000 miles and wondered if I should replace the chain. I decided to do a very careful inspection of the chain rollers, links and pins with the cover off and could not detect any wear at all so I didn't change it.
The timing cover seal replacement is not difficult but involves removal of the fan and serpentine belt. You will need a new camshaft seal (for the distributor drive) in addition to the timing cover seal strip and the special sealant. I ordered the locktite 5900 and it came in a MB tube with a MB part number. One of the keys to stopping the leak to to remove all the old sealant and make sure the sealing surfaces are clean and dry. I used a thin pick to scrape the crevices and corners out. My engine is now bone dry after putting up with drips for years.