Same concern Madda, I used grease and noise went down drastically but only for a few runs. Subukan mo yun silicon oil na ginagamit sa gearbox ng airsoft halos parehas kasi pitch nun sa gearbox natin ala kasi ako mabili dito.

Tingin ko we can make R2 oil sealed havent observed it fully yet. Pero tingin ko its sealed naman we only need to plug the unused 3mm screw holes with set screws. Then use a very thick oil (100wt+) its thin enough to get in between gears and thin enough to settle down by gravity for another cycle but thick enough not to or minimal leak/seep out between bearing and output shaft even w/o o-rings/seals. The next thick silicon oil I can think of is Tire Black ala lang ako time mag experiment sobra busy sa work lately