Awhile back I called Mike at BCS about the plastic bottom track as mine is all but toast and needs replacing, but apparently they were some type of custom order way back when and are unavailable. I would love to find some type of replacement piece that will work. Until then I just stick a strip of foam pipe insulation over the bottom of the door to keep from rattling and banging while driving. The water seems to stay in fine even when the door is out of the track once parked and showering.
Pls let me know if you find an alternate source for the plastic track.