1979 300D vacuum pump probems

[Nate Stanley]

I have a 1979 300D that we purchased early this year. It has a vacuum pump from a later engine (only 1 vacuum line exiting the punp) that was put on it about 35K miles ago. Last week the whole pump let go- upon inspection, both large metal discs inside the pump were shattered, though all pieces are large and accounted for, nothing got into the timing chain..
The follower bearings and check valves are still good. Is this a common failure mode in these pumps?
Should I go back to the original '79 style pump? The previous owner was told that this later pump was the better of the two.
Does anyone know who has the best price on a Mercedes-Benz replacement? The one that came off the car was made in Spain, and they do not deserve a second chance.
Please advise---