Look in the Rong Fu forum, several members have changed out those bearings with detailed step-by-step. I have King PDM30, which I think is the same as yourRF-30, and went for angular sealed ball bearings. Installed them in 2012 and have not touched them since. If your mill has the same quill setup as mine I used FAG 7206-B-2RS-TVP and FAG 7207-B-2RS-TVP bearings. A little narrower than the original open taper roller bearings but within the adjustment range of the take-up nuts. No worry about dust, chips, or the grease being thrown out. If that works for your mill I would recommend it