I would pull the injectors and check them. If the tip shows serious visible wear I would put in rebuilds. My one mercedes maint book from mercedes source talks about how to visually inspect them. It is probably best to have a source for injectors near by so if you pull them and they need replaced you can go get them and not have to put in new crush washers to put the injectors back in.

New injectors improve the spray pattern causing cleaner burning meaning more power, better fuel economy and less carbon crap.

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My Daily : 96 E-300 Diesel with 195,000 miles
Retired: 92 300D 2.5 T 345K miles and for sale
Retired: 95 E320 157K miles and currently parked with blown engine

Both retired cars are for sale as is my w124 shop inventory