You should be able to buy one at most auto parts store. They come with directions and can be used for a number of things. You want to use it to pull a vacuum and test the various vacuum systems in your car. The doors and the climate control would be the obvious places to start since there are so many rubber acuators in those systems.

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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