I dropped my phone between the seats and used the power controls to lift the front and back of the seat bottom as high as it would go to look for it.

After getting the phone, the rear of the seat would not go back down. Moving the of the control lever for the rear seat bottom only produced a clicking sound in either the up or down direction. The front of the seat bottom would go up and down normally. The seat would slide forwards and backwards normally.

What had happened is the gears in the seat mechanism had traveled too far when moving the rear of the seat bottom upwards and now the gears were jammed, instead of rolling to move the seat bottom downwards. My guess is that the gears "over-topped".

I used the controls to lower the front of the seat bottom down, and slide the seat bottom fully forward to expose the works in the rear passenger foot area.

On the right side of the seat bottom is a good size black plastic cover. I used an 8mm socket to remove the cover, and used the 8mm again to remove the two screws holding the black steel plate under the plastic cover. This steel plate is a bearing support.

Under the plate is a white plastic part, I pried it carefully, slightly out of position, with a small flat screwdriver to expose the well-greased worm gear and the large gear it engages. I turned the large gear about 1/6th of a turn (top of gear towards rear of car) and could see that the rear of the seat bottom was moving down.

I carefully re-engaged the white plastic part holding the worm gear into position, put the steel bearing plate over it and put in the two screws. Then I put the black cover over the assembly and put those two screws in.

The rear of the seat bottom now goes up and down properly with the control.

__________________
.
1st MBz: 1982 300SD
2nd MBz: 1987 300SDL
3rd MBz: 1995 S420
4th MBz: 1987 190DT
5th MBz: 1984 300SD w/1983 300DT engine
6th MBz: 1999 C230k I'm 3rd owner, got it w/57,235 miles.
and manages Mom's 2007 R320 CDI