I have a 1982 Rabbit convertible that's leaking transmission fluid from the drain plug. It was in storage for years, and came out of hiding last summer. I had the seals on each of the cv joints replaced last summer, as tranny fluid was splashing while we drove. Last week, I discovered a leak and powerwashed it. I then traced it back to the transmission drain plug. I tried to tighten it with a 17MM hex, it's tight. Is there a gasket I need to replace? Any ideas?

Thanks and sorry for the long post.