No need to synchronize the windows on an SL made before roughly January of '94. Also, there is no Base Module in a 300SL. The module that waybomb has located is the OVP, and even if the fuse is good, it's well-documented all over this forum how it can be bad.

The flashing top switch indicates the top controller has detected a fault and set a diagnostic code. You read the code by counting the flashes after triggering a read at the diagnostic socket. You trigger a read by briefly shorting the diagnostic socket to chassis ground for 2 to 4 seconds. If you search the archives under my username, you should find all you need to know.