After reading your post I had a look at my BSA on the air rifle, 4x, and it had nothing of what you described. But I did notice a oily sheen around the AO that I never noticed before. The optics are still clear as ever.
My rifle just stands in the corner and doesn't get a whole lot of attention unless I see an unwanted critter in the back yard.
It makes me wonder if maybe what you're experiencing and also the oily sheen I'm seeing isn't from the weatherproofing process. Likely it is pressurized and that pressure is escaping through the seals.
You know the bad rap BSA gets........ I feel pretty fortunate with the couple that I do have, they work as supposed to for that kind of $. I haven't been out in any rainstorms with them though either.
