I have replaced several of those 3 HP impellers with Sierra 18-3001 with good results on all of them. The only sierra impellers I tried that don’t work good are those for 1974 -1990’s 9.9 and 15 HP Johnson/Evinrudes that use 18-3050 – they don’t pump at really slow back-trolling speeds, even with the new Sierra cup. If I have time to wait, I do order OMC impellers, but usually my Napa auto parts store can have the Sierra ones (same part and number, branded NAPA) for me in a day.
Dave