Originally Posted by BillGrissom

Yes, used vac check valves are priced $100 on ebay. Almost every 1982-85 300D I've seen in the junkyard had that check valve picked. If not, of course I grabbed it. The vacuum pump rebuild kits run ~$200 now. I rebuilt one of my pumps back when the kit was $80. The earlier two-tube vacuum pumps have cheap rebuild kits ($10) and they will fit later cars. Kits for vintage VW diesel vacuum pumps are cheap and a source for the little internal check-valve disks, but they don't have the piston-ring seal (Teflon & O-ring) which is often the failed part.

If you give up on the factory Pierburg vacuum pump due to costs, other options are an electric vacuum pump from newer Euro diesels (VW, Audi), which they use for their brake booster. But you must add a vacuum switch. Some say they might cycle too much in our cars, due to the constant demand by the VCV valve. A few posts here. Another thought is an alternator with an integral vacuum pump on the rear, but looks like it might bump into the motor bracket.