mine do the same, o'rings are still good but over time i think they compress a little
vaseline works well to rectify problem
but food grade silicon grease is better as long term vaseline can harden the rubber
my units are 7 years old and still going
getting picked up in the morning they can sit at depot or in van all day before going on overnight flight
i drop off here in Tga at 4pm and arrive in CHCH at business address before 9am next day
so you are talking importing fish and international flights
with more information the conjecture stops and answers are no longer like winking at an attractive woman in a darkroom