OP, the only vacuum pumps available are new Mercedes pumps. No rebuild kits and the external check valve is ~$80 which is too significant to gamble on something that might not fix it. The complete pump is ~$350.

I will have access to 4 to use as parts if one goes down. There are currently 3 good pumps and only 2 cars so I may be good. The one that failed recently was a relatively new Piersburg which is the original manufacturer.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.