Although it is possible and maybe even likely that this is a simple problem with a simple fix, I think it would be a good investment to find a trustworthy independent shop and have them take a look at it. Like Larry said, if it is a problem with the timing chain then the next failure step could be a very expensive headache.
Or I suppose somebody on this forum could suggest a fix and your problem could be completely unrelated to the chain. Time will tell, but hopefully not in the form of some serious engine work.
1976 300D (W115) - 330K and still going (sort of)
1991 300D 2.5 Turbo - Sold at 221K
1983 280SEL - Sold at 206K
1981 300SD - Sold at 232K