Got a diaphragm-type rebuild kit with step-by step instructions from the Source in Bellingham, WA today, rebuilt the pump, and now it really sucks!
This was my first W123 "roadside" repair (in the parking lot, actually). Another daughter of mine stood by as I worked and commented on the ease of doing the job- everything went smooth.
Having step-by-step instructions (with photographs) for this job made it go quickly- and I realized while driving it home the reliability confidence factor got quite a boost. Since the car had fewer than 5,000 miles logged since 2003, I was worried about any rubber parts that had been in the "deferred maintenance" category before that time. Well, with a good 1" tear in the diaphragm, the pump is now off the "deferred maintenance" list after the rebuild.
The diaphragm was torn nearly straight along the reinforcing cord near the washer.
Now that I have done it, I am going to rebuild the pump on the 240D. The peace of mind factor is important! You can't be driving around with a failed pump! Fix it at home, where the coffee's always hot and there's someone asking you "Are you done yet?" every six minutes!

snapped_bolt

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'81 240D For now, a good place to borrow new parts
'80 300TD Probably will be put back into service!
'79 240D BACK IN SERVICE SINCE 09/16; limited use, oil leak. Guide pin r/sealed/replaced. Still a leak. Front crank seal....