Yesterday I got the antennas taken down from the old house.
The Watson W300 still looked in good condition after over 5 years on the roof (it wasn't new when I put it up either). I'd covered anything that could move in bathroom sealant and none of it had moved. When I first had the W300 up, the screw that would stop the main part of the antenna rotating in its tube had come loose, so I didn't bother putting another one in (I've heard of this happening to other people) and just used the sealant to stick it in place.
The only thing which had started to work loose was the bolt in the middle of a Jaybeam folded dipole, which must have been my fault for not tightening it enough, as aren't these things supposed to last forever in 150mph winds, 300 metres up a mast?