Diffwhen i run a diffi in my 501 i use a durga diff and have never blown oneas for the rear diff there is a lot of bull talked about what to dothe answer is simpleuse 501 outdrivesuse 10 ceramic balls2 steel balls 1 at 12 o clock and the other at 6 o clock ( this cleans the track and helps keep the diff smooth)use only a minute amount of tamiya ball diff grease in the diff or the ceramic balls will slip causing heat build upuse tamiya anti wear grease in thrust race.then cover sides if diff with a sticker or die cut coversi ran half an outdoor season without a rebuild like this and only rebuilt then because i am anal about prepi have never blown a tamiya diff building this wayps this technique came from a trf works driver direct to me with no chinese wispers!!!