I have a 2000 540ia black/gray sport/GPS/shade. I hand wash only too. You are doing the right thing by washing with soft cotton, but I've heard that leather chamois strip the wax off of your car. I use synthetic chamois and it's worked great. Plus, whenever you wash and wipe your car, it is very important that you don't use circular motions because of swirl marks. You need to wipe in straight lines that'll sort of follow the contour of your car, at least that's what I read in a carcare website. Good luck.