I have a 1990 R129 300SL. On particularly bumpy roads (Richmond Mortlake Kew etc) the roll over bar is making an awful lot of leathery creaking noises - quite loud and anoying. It doesn't happen when it is in the raised position. I don't really want to drive with it up. I've tried conditioning the leather, and lowering the ocasional seats but to no avail. Has anyone any ideas about how to silence it?