The process is counterintuitive. I took mine off my 85td without paying much attention and it took me about 10 minutes to figure out how to get the new one back on. Put the metal arm thru the slot and then slide the wiper blade back is about the most meaningful advice I can give. Or, find another car and look at it.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13