Thanks Ch6pak. Some forum members say these cars have many water leaks, this must be one of them. I filled the gap with a glued-in piece of closed-cell foam. Tapered the foam so qtr glass rolls up/down without trying to tear the foam out. Seems to seal well. I won't be rolling the qtr glass up/down much so fix should last awhile. There are other smaller gaps here and there that need to be filled, but this one is the biggest I've found so far.
Thanks again Ch6pak for your help and taking the time to snap & post all your photos.
One last question on a different subject...With door open, looking down at sill plate, at each end of the sill plate the "end screws" fasten into the plastic kick panel and rear qtr panel. Does your car have stamped metal plates that snap onto the plastic panels? These metal plates have holes threaded for sheet metal screws, and accept the end screws of the sill plate.