[V8] Rear differential oil

[Radek]

Hello;
I'm faced with the issue of filling the rear differential from a 1992 V8Q that's being fitted into a 1996 S6.  The specs call for GL-5 SAE90 oil.  There's no mention of synthetic.  What I have on the shelf is GL-5 SAE75/W/90 synthetic blend.   I think it will be fine, but I'm throwing this to the group in case someone knows of any counterindications or peculiarities of Torsen.
Thanks,

Radek.