Our BX2660 had that problem, tubes or bead sealant are the only fixes.There were others about 10 years ago, (myself included), that had the front tires (turf tires) losing air on the BX models. It turned out to be the seating around the rim...right out of the dealers....brand new.. I fixed mine with some rim sealant that took care of the problem.
Cheers,
Mike