Welcome back!

I knew you'd be back to the 3-pointed star eventually...

The part you are looking for is in the EPC, not sure why the counter man could not find it.

I looked against my 87 wagon which should have the exact same engine (OM603.960).
Assembly M - Engine
Group 20 - Engine Cooling System
Section 15 - Water Pump
Find # 146 Gasket, Pipe Socket to Cylinder Head
601-203-03-80 (it's been superseded 4 times!)

Only caveat is that my car has the factory engine with a #14 head so that gasket may be #14 head specific.

BTW the 98 you sold me is running great, I drive it now, my wife missed her SUV too much so I bought her a 2008 ML320 CDI.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech