Ran Napa premium hydraulic transmission fluid before. Seems I have easier shifting with both tractors after I switched to Mystic hydraulic trans fluid both are udt fluid compatible per manufacturers, might try Chevron thc if I find a good deal on it. I do occasionally use Napa Gold filters but they aren't much different in price than OEM Kubota filters. Udt fluid must have gold flakes in it lol, and imo is a unnecessary expense for my old gear driven tractors, found amazing deals with mystic brand fluids occasionally, also servicing them close to specs is probably helpful to keep them running.