I had a similiar problem with my 93 sls.
(Is it just your light staying on or is the brake not disengaging ?)
After putting it in gear the brake light would stay on.
But it felt as though it was realeased.
Every now and then I had to tap the bottom of the pedal upwards and the light would go off.
But like I said it felt like it was released and was no indication of any drag.
Then one day the whole pedal was sloppy. But the light would go out if I was to manually bring the pedal up. And still no sign of any drag.
The next time it was up on the hoist we looked at it and found that the cable was streched. It took some heat and a load of WD but we were able to loosen the adjuster without breaking it.
Once the slack was taken out of the line it would release the way it was supposed to. For a bit anyways. Was certainally better. 98% .
Thats when we discovered that one of the the rear calipers were sticking abit as well.
But they only seemed to stick when using the parking break
Sounds weird I know ?
Anyways......
Im preety sure my 93 had the vaccum as well. Think I was told that here when I brought up the problem.
Apparently is the usual cause.
But for me it wasnt.
So there is something else to look at.
Good luck
