If you pulled the viscous coupling apart enough to get the fluid out, it's farked. They cannot be reassembled.
It's a myth that Sti's had anything other than the standard 4KG/m centre diff or DCCD. None of them came standard with a 12 or 20kg/m diff. When you drive a car with one fitted you'll understand why. The tight viscous couplings were competition parts that were fitted after the cars were made usually only for competition use.
I've got plenty of good secondhand late type 4kg/m couplings if you want one. $180.

there wasnt really any fluid in there. was more like a grease and there wasnt much there. it was very thick.

what are the ways to identify the type of coupling? because i really would prefer the same that was in there, whatever it was. there was a 6 digit number on it, does that mean anything?

Some have engraving on them, others have no identifiable markings. I have a cut off shaft I mount them on and feel the effort requred to turn them. Highly techno stuff, but a stock 4 KG can be turned with one hand, 12 KG takes a fair effort, 20 KG and you need to be Arnie Swarzenegger. I've tried using a torque wrech to measure them but it's way too variable depending on the speed you turn the shaft.

It's too late to measure the one you pulled apart, but unless somebody put it there especially for autokhana in Japan, chances are it was a 4 KG/m.

The car is a australian delivered sti, so it would have the stock diff. proberly 4kg. i guess the 12kg diffs are hard to come by?

Yeah, you can buy them brand new, there are 2 different types (early and late) they sell for about $1600 new from memory. Yours will require a late type. Leigh at RMS had some used ones for sale a while back at $900 ea. maybe still has them? I can't recall if they were early or late though.
Otherwise let me know if you want a good stock one cheap.