Jonsered/Husqvarna Fuel Vent "Plugs"

[Snojetter]

I've got 3 new-to-me saws that I just noticed a common issue. Two are Jonsered 2150's, the second is a 2152. All three of them are missing the pair of vent plugs that go into the side of the fuel tank underneath the carb. These are very small white puck-like "plugs" that just slide into the plastic housing; I assume they are for venting the tank, but I do know that filling the tank with them absent leads to plenty of spilled fuel. As far as I can tell, they are just supposed to slide in. There doesn't seem to be a lot of friction present to keep them in place. I installed new ones and on the exterior plug, I dabbed a very small amount of trim adhesive just to create a little "ridge" that would prevent the plugs from falling out. I've run a couple tanks of fuel since that "fix" and so far they haven't moved. I didn't "glue" the plugs in...but I'm wondering if there is some sort of adhesive that should be used or if they are meant to be held in by friction alone. Anybody else seen these plugs disappear and what have you done to prevent that?

I'll throw out a couple part numbers in case it helps:
501629801 - valve plug
503600401 - filter plug

Thanks!