OM603 oil level sensor seal?
 

On a 1987 300SDL. It was leaking badly when I bought the car, so I replaced the O-ring with a new one from the dealer, and if anything it now leaks worse. What did I do wrong? I got it at least reasonably clean, and I couldn't see any damage.

I could have sworn they had two seals, but that is probably incorrect since I resealed mine over 10 years back.

Sensors themselves and do leak. I cannot imagine a fresh one running more than $50 for a good brand. Torque is probably quite low, fasteners are M6 from memory.

oil level sensor plastic fatigue or have hair line cracks. A lot of the time is the plastic around the middle connector. You need a new one. Alternately is to degrease the middle and fill it with rtv. It will buy you 1 year or 2.

Get the real MB sensor. Don’t mess around with the aftermarket one or you will be doing it twice. BTDT.

You will have to get the o-ring separately with the genuine MB sensor. The aftermarket one includes the o-ring.

When I installed the aftermarket sensor I saved the MB o-ring I had ordered since the sensor came with one in the box. When I had to do it again at the next oil change (it was giving false low oil alarms) I only ordered the sensor from MB. Good thing I had saved that o-ring.

Thanks, I ordered a new sensor and I will try that. A factory one cost $58, so not too bad.