I still have the solid tires but it won’t work with rim for inflatable, when using old rim it won’t fit into the new landing gear axle. I’ve got this new landing gear set because my old one was offset. One gear or maybe both mains are suspected to be few quarter inch behind the original distance. This would give me a hard time on taking off on the grass field as my preparation for Florida Jets on that time. The gear is better than old one because it has bearing rather than bushing. There’s no more play on the wheels and nuts are tight very well. I have only one issue and it’s the same as yours on one gear. I didn’t noticed earlier that it contributing problems on takeoff with side wind and worse on landing. Found out that one tire has lower pressure. Fill it up to 80-psi to compensate and few minutes later one wing is lower than other and that tire has no more air. I vulcanize it while awaiting for parts and it work with the use of CA glue and tape. If it’s on the o-ring those above suggestion should be working. That's why I suggest to put under water to find out the cause of leak. Silicon is also works very well while you’re awaiting for replacement o-ring. On the bigger o-ring on the center of the rim where it seals the air inlet valve use o-ring lube. If it's one the side of the rim or tire edge you may use gasket sealant. Tar is the last resort.

Now I replaced it with the new one. Forgot, it was the $16 one (AP-ITR7683).

Here’s my new gear in action:
http://www.youtube.com/watch?v=KWIsZruIWFE