I had a similar problem with the driver's seat on my 87 300e. When I lifted the seat up it would tilt toward the console. The MB dealer said a cable needed to be replaced. When the cable came in, it was the wrong one.
The tech working on my car remembered having this problem before. He removed the seat pull cable for rear height adjustment,filled it with grease and re-installed it. He said it may last for a day or it may last longer. That was back in March of '99. It has worked fine since.
I'm not sure if this will work for you but it may be worth a look.
[Edited by donwo on 03-12-2001 at 10:11 PM]