04 RX8 MT, use for pleasure driving, solo events, and track days. Looking to change tranny and diff oils and considering synthetic, specifically Royal Purple. Book calls for 75/90 in trans, straight 90 in diff. Would appreciate any comments re: experience with RP lubricants and whether or not I could use the 75/90 in diff also.

Thanks,

Loran Keller

 

I use Mobile one. Works fine, even on the track.

 

Not sure I have heard of Royal Blue?

Eunos is probably the best, but it's expensive and can be difficult to get.

Redline MT-90 is the most commonly preferred fluid on here, as it's reasonably priced and easily obtained, while still producing excellent results.

Royal Purple shows up too frequently in transmission syncro failure threads for very many people to be comfortable with using it.

 

That's the same conclusion I came to after reading a lot of old threads on there. The safe bet is Redling MT90 in the transmission, and Redline 75W-90 in the differential. I've got about 25k miles on these oils and haven't noticed the deterioration the OEM oils had over less miles.