300sl ride height
 

I have a 1991 300SL with 18inch AMG wheels and 40 profile tyres The wheel rubs on the fender when turning. I understand MB have shims or spacers at the top of the springs, could a previous owner have removed these to lower the car. Can they be purchased and replaced or do I need new springs.
Or, is MB suspension prone to sagging with age.

I have heard that the 129 can sag, but honestly I think your wheels are too big. The 91 300SL came with 16 standard, so you might need to add some shims to raise it a bit to accomadate those new wheels and tires. So it is likely the wheel size rather than the ride height. Happy Benzing!
Brian