Cliffy is dead on !!! Listen to him.
Never reuse any fluids in your Mustang, Replace them while its apart.


IMO... I like the Mobile 1 Synth AFT ..I don't agree with all the hype on RP.
Mobile 1 is the only stuff that goes into my Ponies (Motor-Tranny and now in my Diffs)

BTW Cliffy TY for your help in the past,I did decide to use the Mobile 1 70-140 when I replace pinion seal ( I know you said use MC )
Also didnt use any FM with M1 synth gear oil and its been great No chatters at all on cornering.

 

I had used RP Synchromax for 70k miles on my '03 GT (changed at 30k and 60k) because I could get it at cost from a friend in Daytona--the recession hit him hard so I got M1 ATF from Autozone.

FWIW--I have got to tell you that it blows the RP out of the water, much smoother shifts and th 1-2 "notch" is barely noticeable...

 

i spoke with walt at promotion powertrain and bob hanlon at hanlon motorsports, both have said synthetic blend for the 3650 is too slippery for the synchros which is one of the reasons my 3rd gear went out twice, needless to say bob hanlon is in the process of building me a fresh upgraded 26 spline 3650 and i will be going with the fluid he tells me, that guy knows his sh*t and wont rip you off

 

Re-use the fluid, wtf? Would you drain your motor oil and then put the used oil back in? Never re-use drained fluids...

I use RP in my trans and my diff and have been very happy with it.

 

Kinda OT here but goes along with the used oil thing. I was at Autozone last night and see a Green Valvoline Oil Jug so I read it and apparently it is Oil made from 50% recycled oil. I'm not sure I'm ready to used recycled oil in anything yet
It's Valvoline NextGen if you want to Google it

 

Any time you drain your trans always replace the fliud with new.