I had mine replaced. The inner bearings exist! Believe it or not, they're interchangeable with Mustang II bearings. The inners should come with a grease seal and the cheapo ebay seals don't. Get quality seals. The outers are easy but for the inners you have to take it all apart and get the hub off. My inners looked fine, my outers were blued from heat. I can't imagine them going bad unless your racing causing 2000º heat so be sure you need them before you dig in.

Les