I have a 1999 E320 Avantgarde. Great car, despite needing a new gearbox at
115,000 miles.One really annoying problem though. The passenger side electric seat (on the left as right hand drive in the UK) squeaks and moves from side to side when going over rough surfaces. I cannot see a way of removing the seat back without damaging the leather facings. I am sure there must be a way of tightening the bolts inside the seat back to prevent movement but no idea.
Mercedes dealer says that they would only be able to replace the seat, not repair it.
BTW M-B dealers in the UK are amongst the worst.