Vacuum pump a cinch to repair
I would rebuild the vac pump before thinking of replacing it. I to own an '80 300TD that had a bad vac diaphragm which I purchased on fastlane for about $8.00. There was nothing to remove except the pump housing itself. No need to remove the fan or any other item if you have just a few more minutes to spare taking your time to undo the metric head bolts that hold the vac pump cover in place. The reason the valves seem to go bad is that folks forget that once the diaphragm gets a tear or hole in it, it immediately starts drawing oil into the diaphragm section as well as through the valves. If you use a carb or brake cleaner once the housing is off on both sides of the valves they will hold pressure as they were designed to. Ensure the remaining spray cleaner is totally dry before assembly to get rid of all the oil residue.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan