Sounds like a vacuum issue with both problems related. I don't know how the vacuum system is set up on non-123 cars. Shut off valve is not hard to replace on a 617 but the problem is usually elsewhere in the system on 123's. A quick test is to put a Mity Vac or your lips on the vacuum line to the shut off valve, pull a vacuum and see if it shuts off promptly. If it does, the shut off valve is ok and you have a leak elsewhere.

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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