Yesterday, without warning, my '91 300d starts shifting hard. I've yet to double check vacuum lines or the output of the vacuum pump. In the reading I've done overnight, seems that I have the original vac pump (crimped on cover). Here's the dumb question:

Should I forget trying to diagnose the pump and just replace it as a matter of course? The car has 125k miles. I've got to put a new radiator in it this weekend anyway and it seems like a good time to do it.

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1991 300D 2.5 "Rocinante"
2002 Golf TDI "Teen Spirit"
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1984 300D
1966 Mustang I6 3sp
1985 Mazda RX-7 GSLSE
1982 Toyota Supra
1977 Datsun 280z
1971 Datsun 240z