What's this reservoir R129 94 SL320

[RichardF]

I've been under the front bumper fixing some faulty wiring on the drivers side fog lamp and notice a nearly empty reservoir below the washer reservoir. Any idea what it is?
The washer reservoir is full, this lower one has some dregs slopping about in it, they dont's seem to be connected. Most intrigued.

SL 320 "94" R129

 

[whitenemesis]

Vacuum reservoir?

Cooling overflow reservoir??

 

[RichardF]

Got it. Cooling overflow reservoir