Hydraulic brake servo fluid?

[o0Mouse0o]

I'm finishing a kit project using a Audi hydraulic brake servo.
The Question that has stumped me is what fluid is in the servo side of the unit?
I can find references to the pump being a dual pump shared with the power steering and some schematic drawings that appear to list the breaking side of the pump with a separate fluid reservoir for the servo but little as to whether it is Hydraulic power steering fluid or braking fluid used to power the servo side?
What I do know is that if I continue and fill it with the wrong fluid the seals will be destroyed which is an expensive way to learn.

Photo attached if it helps.

[zollaf]

what car did it come out of, looks like an audi 80 coupe. if so, thats the one with the hydraulic' grenade' pressure resevoir, in which case you want the green mineral fluid for power steering.

[o0Mouse0o]

I think it was from a random ebay sale. But Audi 40 rings a bell.
Thanks for the tip, I'll know not to put brake fluid in it as that would probably be a quick end to all the rubber in it.