Old thread but I'll add my 2 cents. Front left window wouldn't go up on my daughter's 84 126. Sprayed a bunch of electrical cleaner in the cracks around the edges of the switch, let it sit for a couple of minutes and it worked. So I now have this idea that rather than disassembling the switch it might work to drill a hole thru the plastic and spray cleaner down inside on the contacts. May try 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