I think HenryJ will chime in here on this as I "thought" he had seen this on his window or at least the caulk to prevent it.
On mine there is a caulk on the lower rounded glass corners sort of sealing the glass to the frame. That was there before I owned it. I believe it is there to prevent exactly what you found. Some how the seal is weakened between the glass to the window frame and water finds it's way thru this area. Sealing the window to the frame has been the fix in the past.
If this does not sound like what you have, then need a pic or 2.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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