Later model 123 window switches are already LEDs.

I have a 240d so the climate control is different than yours. Mine takes 5 wedge base bulbs like the cluster, 3 behind the knobs and 2 behind the panel.

Spider also takes a wedge bulb, but you will need an LED that delivers light 360 degrees about the axis. That might be tough as I would imagine most of the wedge LEDs are set up to emit off the end.

I took apart my spider, cleaned both ends of the fibers with a q-tip dipped in alcohol, and also gently cleaned all the rocker switch faces the same way, after a fresh OE incandescent bulb it was like night and day.

__________________
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