The vacuum distribution has hard nylon tubing and rubber hose connectors. For the hard tube, I have a bag of tubes from the junkyard or when I stripped the EGR controls off. For the rubber, I use silicone tubing that I have lying around, usually 1/8" size (3.2 mm), and blue to look purty. Some nylon tubes in my 300D are larger diameter. I have a roll of 6mm silicone hose, but don't recall using on the M-B. I also have a bag w/ M-B rubber tees and elbows. In sum, I use what I have that fits. Silicone should last much longer than normal rubber (nitrile?).

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans