Does anyone have any documentation from a sealant mfgr that polysulfide won't remain sealed if it's not constantly in contact with gas? If this is a real hazard, surely the mfgrs would document it. I'd even expect the FAA to be speaking up, with AD's and advisories. There are thousands of certified a/c using polysulfide in their tanks (and to seal their fuselage pressure vessels), and many are decades old & sit unflown for months or years at a time.
I've got a -4 that was built in the early 90's. The sealant is soft in places, and I've had a few leaks. The original builder had leaks, too, when the plane was young.
I've resealed small leaks in the root ribs (at the nose reinforcing angle) of both tanks, from the outside. When I did the repairs, I removed as much of the exterior proseal as I could, and then tried to clean the area with popsicle stick scrapers, picks, etc and MEK soaked bits of paper towel, etc to get into the crevices. Then applied new proseal on the outside of the joints & over the rivet heads.
One side is still holding up fine after 3 years; the other has another leak near the top of the angle. The plane often sits for a month or more at a time, and usually with less than full tanks.
After doing the repairs, someone mentioned that it's difficult to 'contain' the effects of MEK around cured proseal; that it will damage sealant near where you're actually working. I don't know if that was my problem, but I'm suspicious that it was. My next attempt will involve mechanical removal, followed by something that will clean the surface but won't attack the adjacent proseal.
Since one side is holding up, and the other isn't, I have to blame my technique, on the side that isn't holding up.
My totally unqualified opinion is that leaks are 99%+ due to contamination of the surface being sealed. And an in-use tank is a lot harder to clean properly than a new one.
Just my no major motel chain last night opinion. Always happy for new data, with supporting evidence.
Charlie