I've had to reinflate it a few times already and it's only about 4 years
old. Not every time, but it seems like after 6-12 months, it's flat. I'm
looking whistfully at Harbor Freight ads for a 10" wheel for $5 (don't
know if mine's 10", though!).

It's a Union Made (I think that's the brand), the big one (6 foot?). Is
there something I can do to make it not leak? I use one of those plastic
valve caps already. Thanks.

Dan