Taking off the pump is pretty simple. After the recent failure off my pump destroying everything in site including the gear on the injection pump I would investigate it. Mine must have ran a long time with the roller and bearings gone and it still had some vacuum.

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Ricali

03 C240 4matic wagon
95 300E 234,000
7 prior 240;s 5 still going
81 300sd gone
65 230sl gone
49 Studebaker Champion
90BMW convert.167,000
60 Dodge D-100