I have a Walker and two Toro ZTR's that all have slow leaks in the big back tires. The Walker also has two front tires that will not hold any air for more that 2 minutes. I've seen the solid front tires on the Walker website.....anybody used them? I was in Northern Tool today getting some safety glasses and earplugs and saw this stuff called Slime. Anybody used that? Anything better? Similar?