What are you calling the pump gasket... the pump-to-block mating surface or the shaft seal? I too can't imagine a coolant-to-oil leak at the water pump (no possible leak path). It seems that the water pump is going south and needs to be replaced. (Lucky for you that you're just about to retire the car for the season and can do everything needed to fix it without rushing!) Check Fastlane on the top of this page for replacement water pumps. Or since you have time, sometimes you can get a deal on eBay for a water pump. After 164K miles, you won't be wasting your money replacing the water pump, which is a consumable item.
95 E320 Cabriolet, 131K