My bet is on the fact that it's not completely seated into the brass port block. Normally when removing liners from Crowns, one marks where the brass nut is on the liner before disassembly. This at least gives something to go by for depth. As stated in previous posts, it is somehow separating from the seated position in the brass port piece. The O-Rings/brass nut should be tight enough to compress the O-Rings to stop any movement. It's not supposed to be lightly tight, firm is more like it. Gorilla tight is too much. You also may try using Viton O-Rings as they are somewhat stiffer, though I have not had issue with the factory O-RIngs.
mike