You could use a fueladditif from Marly if available in your country.
But as these products are very effecif it is NOT impossible that
some trash could do (a lot of) damage to valves and valve seats etc.
Guess how I learned about this...
So far better and wiser is to find a specialist's (a real one!) advice.
Maybe it is as simple as leaking valve stem seals, VERY common on the
becoming older, hydraulic adjusted valves in all the W124 engines.
Good luck and keep us informed!