I guess it depends on how anal you are, and more importantly how much time you have. I'm nutty about things being clean and how my cars run. I've had my head stuck in engine bays searching for vacuum leaks to solve idle problems or hissing sounds that drive me nuts. But to me, once I found and replaced the vacuum line ( I just did one which was way down there and little-you could barely see it) it felt oh so good.

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1994 C 280 117.5k, White (Good as new)
1997 Toyota Camry 149k Miles (Not so pretty anymore)

1990 190e 2.6 95k (Sold-Should not have)
1981 240d Stick ??? Miles...sold