I let mine go until I had to top up the fluid every other day. I had my local Tech do it for me, no lost time/use of car. In and out in one working day (while I was working) for about $300.00 parts and labor.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.