Well, I dammed off the end of the track and flooded it with silicone.

It rained again today, and the leak is still there.

Since I have the liner pulled forward I can see that the rear cab wall is dry, so it isn't the window.

The water is definitely coming into the back corner and running forward, as today I got out early and checked after the rain... the back corner of the cab is wet, but it wasn't enough to run forward onto the floor pan.

The only thing I haven't sealed in the back corner is around the vent on the on the jam (below the striker).
Is this a possible leak point?