Try a search for "coolant in the washer resevoir". I recall not too long back someone had the heating element in the washer resevoir go bad, dumping coolant into the res. Sounds like you might have a similar problem.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.