I've replaced mine on my W126.....not much fun, probably even less so on a W123 since their tunnel is so narrow. At least there's some room to work on the W126.
My old unit's diaphragm had ruptured suddenly one day, so I put in my spare and all was well.
The plastic thrust pin did break (or was broken) and I had to fish it out with tweezers. I had a new spare one though, thankfully. (its always good to have an "inventory" of parts available)
Some fluid leaks out too, maybe 1/3 a quart......its gross.
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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)