Thanks for the info on the product name - "Dicor Non Sag". Is there a equivalent Home Depot type. Shipping or traveling to a RV store is more expense than the product.
Path1 - Yes, I agree with you best move is to remove and repair. However, I believe I have the location of the leak and if I caulk that location and it stops the leak then I have time to prepare for a removal and replacement/repair of the complete rubber sealing ring.
It appears that the sealing ring slipped slightly out of position during the original installation and left a gap along the top edge.
Regards
MrBHamilton