I'm very familiar with this problem. My car is a 73 280SEL 4.5 with the same D-Jetronic injections system. The car would run fine and then suddenly the computer would tell it to run super rich and it would run like crap. This would leave gas in the oil. Over time the car would get harder an harder to start. I disconnected the trigger points at one time and cranked the car. When it fired, it took split the muffler wide open.

I got a computer from the junk yard and replaced mine and it's been running fine since.

I would be skeptical that the leaky fuel injectors would leave so much fuel in the oil. it should only leak whatever is in the fuel rail which should not be a lot. Now everytime I see a D-Jet computer at a junk yard, I grab it.

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With best regards

Al