the body of the injector can crack and cause leaks, in which case they must be replaced. Not cheap.

Seals are easy, and what looks like a dripping injector can easily be a vac leak on several others, with the CO set at the tailpipe -- the ones NOT leaking air from bad seals will show up rich on the plugs as though they were leaking.

Leaking hoses can be replaced (see the kit on FastLane).

Ignition points full of crud will cause misfire, but if you start and run, the switchbox is OK. Bad primary resistors, on the other hand, will cause weak spark from low current flow to the coil -- check the resistance and replace any corroded or cracked resistors -- on the W108 they are on the driver's side innner fender near the rad, don't know where they are on the W116.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!