I'd leave the water pump for now. When you get the heating problem fixed - add some water pump lubricant to the antifreeze and it will stop the squeal. If the pump was bad - you'd have overheating all the time (worn out vanes - broken vanes would be clanking in pump) or it would be leaking - so I'd leave the pump and get the rad done.The chemicals they sell for DIY are not strong enough for real bad clogs. If they say they can't clean it because they can't take the top and bottom off to rod it - look for another shop - up here in no-man's land - there are shops that have the gaskets and expertise to remove the top and bottom plastic covers and replace them - there must be one down there. Be advised that it might be cheaper to buy a new rad then pay what some of these rad guys want for cleaning. I checked out the price for my 1930 Chevy rad CORE ONLY - not soldered to the top or bottom pieces - $500-700 USD! Mercedes is sounding cheap for rad prices now!!:p :p :p