Remove the filter canister.
Check that the o-ring is still in position.
With a finger tip apply a -small- amount of petroleum jelly, or even vicks vapo rub or
even a teeny bit of chap stick lip balm to the surface of the o-ring.
Replace canister and tighten normally.
Test for leaks.
Have a cold one to celebrate!
This camping stuff is "such" hard work!!