Better to use a bit of food grade lube, Vaseline will over time cause the rubber in the O-Ring to break down.
Always a good idea to have a look at the top edge of the fermenter, there are often a couple of little feathers of plastic where the mould joined, they can create a path for the CO2 to get out without forcing its way through the airlock.
A fine smear of lube on the top edge will do wonders, as the lid is being screwed on the O-Ring is being pushed down and sliding along the edge at the same time, without any lube (even a drop of water helps) it can pucker again creating a space...
Airlocks not bubbling is a perennial problem and its not in the least important. What is important is that the CO2 can get out and that bugs cant get in. That said its very satisfying to see it start glopping away, that yes its working moment.
I routinely use a plug of cotton wool in a bottle fermenter, Gladwrap as above works, as will a blow off tube and a fair number of other options (years ago I was using a piece of an old sheet (well soaked in Met) on an open SS fermenter), just keep bugs out and your a winner!
Mark