I'm not a Merc mechanic but I have made my living spinning wrenches for a long time. If your belt is hanging 1/2" off an idler pulley, that is probably the source of your problem. Pulley alignment is important, the belt must be properly supported. I would carry a spare until you get it fixed, cause its only a matter of time before it lets loose. Make sure your service visits are well documented, if no repair is made, have them document that. That way if you have a related problem once the waranty is up, you will be able to prove it is an unresolved warranty issue. Call Merc and ask who in your area they would recommend .