have the same problem and also have purchased three caps trying to correct on two different blowers. Dealer says it is a problem with the vent design and when gas is splashed around in the tank is leaks back through the hole where strap is attached. yes it could be safety issue but leaking gas burning holes in customers gtass and stinking clothes makes this the last Huskvarna blowers when updating equipment.
Do not have answer but have the same problem. Have bought 3 caps hoping to stop leaking. Removed plug in the middle of cap and put bolt through cap to plug vent hole, starved for gas and had to constantly loosen to use. Blowers is good but gas cap makes it a game changer for me. Have a business and use blowers. At this point I have very poor review of Huskararna and would not recommend to anyone.