[AT] Semi-OT Dixon ZTR mower front tires

[charlie hill]

Guys I've got a Dixon Commercial grade ZTR mower.
The front caster wheel tires are 11 x 4-5 tubeless.
All of a sudden last fall I started having the front tires
go flat.  They are in good shape.  I finally, early this spring,
took them off the rims and wire brushed the bead of the
rims to remove what little bit of surface rust and crud that
had built up and there wasn't much.  Then I cleaned the
bead of the tires with a solvent type cleaner that I hoped would
soften them a bit.  I put them back on the rims and pumped them
up and immersed the entire mess into a bucket of water.  NO leaks
on either tire.  I put them back on the machine, mowed the yard one
time and the next time I went to the mower they were flat again.
So, I got some beat sealer compound and put on the beads.  Same result.
Has anyone got a clue how to fix this problem?

I'm thinking tubes or just having the tires foam filled.  Opinions welcome.
Also does anyone know what size tube fits in an 11 x 4-5 tire?

Thanks, I'm sick of pumping those tires up.  The only leak I've ever found 
was
around the bead.  I'm pretty certain there are no holes in the tires.

Charlie