i have an 06 mcs with limited slip. i am leaning towards royal purple since i have a $50 coupon from advance auto and they carry royal purple.

what are you guys running in your transmission?

 

The viscosity of Synchromax is too low. Redline MTL or Neo MTF are better options.

The factory fluid is a pretty decent synthetic so its unlikely there will be much (if any) improvement.

 

I don't have a lsd, but I went with the Redline MTL.

 

iv seen a lot of people using redline but dealership fluid is what i always use

 

I think if you do a quick serch you might find a few post about one of tge two royal purple oils mentioned, it is fine for summer, but thicker than spec for winter...resuling in stiff sgifting, and about a half mpg loss. The post did say their online listing for which to use did not list the mini as compatible....
Biggest thing is to find the right viscosity...older manuals used like 90w with lots of zinc as an anti gaul agent....nwer mtf specs have thinned the oil a bit to eek out a few tenth of a mpg.
Tip...google site serch is much better than the built in one here, and it should have all the info needed. Just rembering this, and would do it, but on my phone.....

 

Motul Gear 300 75w90 ftw...i went from stock to Redline to Motul and i can say that the transmission shifts like butter