Cat Tracks have plastic or nylon needle type bearings, about 1/4" diameter and about 5" long, I would guess maybe 18 or so per hub, they do not fail as long as you keep the cotter pins that hold the end plates on in good shape. They might get some sand in them when launching in surf, by you can easily wash it out in the water or with a garden hose, just roll them under water and it washes out.

The only problem I've seen is after many years, the big black rubber tires may start to leak (or maybe it's the valve stems) and you will have to use a bike pump or gas station air hose, but be carefull not to overdo it, and pump them up. I have not had to put any air in the ones I bought new a year ago. The last set I had was about 8-10 years old and also held air pretty long (2-3 months) before I had to put any in.