You need an adjustable toilet wrench available at the hardware store for about $10. I've got some posts and a picture on here somewhere. They look like a giant adjustable wrench with a locking wing nut. You set it to the size of the hex nut, put it vertically down on the nut and use an extension thru the hole in the handle to turn 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