I've had the slow reverse thing going with my 300e for 5 years now. I wouldn't worry too much about that.

The clunking is probably the flex discs. The front one is the first to go bad. Look at those ASAP..

It should hold out for much longer before overheating. Even without a fan working. I would do a coolant flush, and definitely get the aux fan going. The mechanical fan helps, but the electric one will keep you from overheating.

Oil pressure Sensor is tapped right off the oil filter housing. Trace the wire as its likely the culprit. I highly doubt the sensor failed. I would bet the wire is to blame.

Stiff brakes are a vacuum issue. If you don't own a mighty vac, I'd buy one. The car will run much better when there are no vac leaks.

Good luck

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2