Washer fluid itself can leave residue which over time, 20+years, is enough to clog the system. Some say its best to just use water (distilled I suppose).

I've attempted to fix my wagon's rear window washer. Pump works, but no amount of needlework, etc has freed the nozzle. Next thing to try is remove the nozzle and see if I can get fluid on the nozzle end. Ever try removing the nozzle on a wagon? I have no idea and it's not a job I look forward to doing...

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1982 240 D, 308,000 - 321,127 miles (sold)
1982 300 TD,166,500 - 226,000 miles
1998 E 320, 120,000 - 144,000 miles
2005 C 230 K, 26,000 - 77,000 miles (sold)