Ford XT-M5-QS manual tranny fluid

[Cosmic Wonder]

Ok guys. I've been searching all over the web and this site for a straight answer but haven't found one.

I previously owned a 2008 MS3 and a ton of people swear by this tranny fluid for much improved shifts and feel. So, I am curious about trying it in my P5 to see what it'll do. I recently purchased my car and am doing a bunch of stuff when I can since I don't know the whole history of the car. Now, I know the P5 manual states a API service GL-4 or GL-5 fluid, SAE 75W-90. The Ford fluid is also a 75W-90 but it is for use where GL-3 or GL-4 type gear oils are used. So, I think it is compatible, but is it? Obviously GL-4 is stated in both the P5 manual and the fluid specs but is that overlap (GL-3 vs GL-5) acceptable?

http://www.fcsdchemicalsandlubrican...ransmission Fluid&category=Transmission Fluid

 

[Stickman]

The higher the rating, the more sulfur additives, which create greater pressure protection, but which also cause deterioration of yellow metal (brass) parts, usually synchros.

My understanding is that our trannys don't have yellow metal parts, so higher level service designations may not be an issue. Others here will know for sure.

Some people (even a dealer) say synthetic will cause leakage problem. I've had no problem w/ Valvoline synth for 1.5 yrs now.

Don't know about the Ford product, but the included link will give you some background in lubes and how hey stand up tp wear.

www.sinwal.com/data/The Study Of Automotive Gear Lubes.pdf