I have seen several of these electronic throttle actuators that 'failed' on dissection (I'm an engineer, and have an SL 600 with 2 of these things to fix). found the wiring insulation had disintegrated inside the cable housing.

The failure is not 'inside' the actuator, but in the wiring harness going to it.

MBZ and Bosch are aware of the failures, but are not doing anything to recall or assist owners in repairs. The root cause is faulty plastic insulation , just like the main and engine wiring harnesses. This problem is in ALL MBZ with electronic throttles from 1991 to about 1997 I believe. The cost to consumers averages over $4000 for the harnesses and actuators.