As far as my experience with a 95 E300D I bought that had the replaced wiring harness - its still holding very well.

If you feel that the car is underpowered yet after replacing the wiring and everything checks out OK, test the errors (I dont know if your car can be interrogated and logs pulled - CAN BUS). The Electric throttle actuator can also go bad internally, it uses the same crumbly wiring inside it too.

A competent automotive electrician can rewire it if the PCB and its motor are good otherwise its a steep expense.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)