Water finds many ways to infiltrate and can track in strange ways as well as you already know. If the window tracks are dry can you tell if the water is coming from underneath the driver window track inside plastic edge wall flange?
If yes, it is possible that the window frame was installed poorly or with inadequate caulking or water seal material at the factory. It is also possible that the caulking on the exterior of the window (especially on the top and side edges was inadequate or has degraded so that water is getting into the space around the window frame and coach wall and traveling down the exterior window track inside the wall and exiting from the lower window track flange between the coach wall and track flange. It is also possible that it is coming in from your side mirror and traveling.
The easiest and cheapest first fix to try IMO is to re-caulk the exterior driver window flange edges where it meets the exterior wall of the coach on top and sides in particular. This will help prevent water from getting into the window track frame in the first place. You could also inspect and re-caulk around the driver side mirror mount on the exterior coach wall as well. This may not immediately stop the drips inside because rain water may have filled up some areas between the window frame and inside coach wall and will continue to migrate and drip for a while. The main thing is to stop the exterior infiltration ASAP and the inside accumulation will dry up and stop within a few days I would expect. If re-caulking on the exterior window and mirror trims stops your drip situation, then it would be worth inspecting all exterior window and other device (i.e., light fixtures etc.) trim caulking to make sure they are still well sealed.