The 123 was notorious for bad window seals. 123s have the old school H-shaped gasket that catches the edge of the glass on the inside and a metal lip on the outside. If the gasket fails, the metal lip gets eaten by rust and you get a nasty leak.

On newer cars the window is glued in with urethane adhesive.

Also check the antenna gasket, those are prone to leak and are easily replaced. But usually you only get water on the antenna side when that happens.

__________________
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