I've seen and heard a few things about the vacuum pumps on the W123s, mainly having to do with the difference between the 1-valve and 2-valve models. I'm just outright confused now. The two-valve version has a line coming from the air filter to the pump, then a line going out. The 1-valve just has the one line going out. What gives? Does the single-valve model pull unfiltered air straight from the block? Furthermore, my car (see sig) has the 2-valve while my girlfriend's car, also a 79 but with an auto trans, has the single.

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- 1979 W123 240D 4-speed, 390k miles