I did a fair bit of searching on the issue.
The car is a W202 (94 C220).
The driver seat won't move up/down anymore. I can hear a grinding noise from the motor, but the seat won't move. All other power functions are fine.
There are 3 identical motors under the seat, bolted to the left side.
I've located the motor for the up/down function, it's the one at the back.
Since I can hear it, I'm assuming the problem is with the motor rather than the switch or wiring.
Does the whole group of three need to be swapped or can the one motor be replaced or fixed ?
Each one has the same P/N: 202 820 0942, I could not locate it on fast lane ?