The problem with after market parts is not necessarily reliability so much as compatibility. If it's a filter is the degree of filtration the same as the Kubota? Is the relief pressure the same? It's not just about whether the filter will fit and not leak. Fuel and air filters should be less of an issue. For the difference in price I'll stick with Kubota, though. My tractor was a big investment and parts aren't cheap. For an HST transmission I'll stick with Kubota fluids. I'd be less concerned about a standard transmission and probably just use a good grade of hydraulic fluid as I've done with my Mitsubishi.