Definitely the thicker oil. You might even consider 75w-140.
Have you rebuilt the diff with new clutches? I'm not sure how the small case will hold up to the M52 on track. When I rebuilt my medium case diff the clutches were toast and that came from a E30 325i. Last I checked thayermotorsports has the small case clutches and can recommend fluids. __________________ ~Dave~
98 328ti Morea Grun slicktop
11 128i space gray slicktop
13 JGC WK2 Deep Cherry
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