Good Used Vacuum pump checkvalve. FITS THE FOLLOWING: ALL 123 and 126 chassis 240D, 300D, 300TD, 300CD, and 300SD 1980 to 1985 with later style vacuum pump (only one line coming out of top). You might consider getting a spare while these are still available. YOUR VACUUM PUMP WILL NOT WORK WITHOUT A GOOD ONE!
In 1980 Mercedes changed the design of their diesel vacuum pumps. Instead of a rubber diaphragm pumping action they designed a piston with an 0-ring seal to replace the diaphragm. This design is inherently more reliable but there seems to be a common weakness in the pumps installed on four and five cylinder diesel built from 1980 to 1985 (excluding the 190D).
To determine which type of pump you have you can check the following: Older style pumps have two large vacuum lines attached to the top of the pump and this newer style only has one.