I just bought a new SL this week and the cream carpets were filthy. I put them in the washing machine one by one and they've come out like new.

The foam had already seperated from the back so there was nothing to come off in the machine.

If you are considering new ones it might be worth a try first.

My wife did them on 40 degrees c wool wash.

Don't blame me if yours fall to pieces though !

Good luck.