Car is a 2002 A4 3.0L 6 speed manual, quattro.

I was changing my manual transmission fluid and rear diff fluids today, using RedLine MTL 75W90 GL5 in the tranny, and RedLine 75w90 GL4 gear oil in the rear diff as recommended by the Audi shop.

When I changed the rear I accidentally put in 1 liter of the correct gear oil, and half a liter of the MTL. I know you don't want to use a GL4 in the transmission because of the synchros, but wondering if there might be any harm caused by the half a liter of GL5 rated oil in the rear diff?

 

I believe its the other way around; you do NOT want to use GL-5 where 'yellow' metal is being used, like brass syncros....

http://www.stealth316.com/misc/pennz...oilsummary.pdf

Mine says GL-5 is ok for front/rear, with GL-4 for the center and GL-4 for manual trannies. All Synthetic.

 

See I'm even backwards about being backwards. You are correct, and I used the GL4 in the front like I'm supposed to, but mixed up a half a liter of the GL4 into the rear diff along with the GL5.

 

Was this synthetic fluid? I was just reading up on this issue again, and it seems that most synthetics dont have the issue anymore, and in fact they are starting to use the 'GL-4+' or 'GL-4/GL-5/MT-01' labeling to announce this fact.

So, in the end, it'll be ok...