While playing in the snow I discovered that only 2 wheels were spinning, which model came with a rear lsd?

 

All turbo Impreza models have some sort of rear Lsd, a viscous type in your case (type Ra & R models have a plate diff).
How fast were the wheels spinning? Which two?
They do wear out, but maybe the rear wheel wasn't spinning fast enough.

 

Thanks for the reply.
I was in 1st gear so not that fast and it was the n/s front and o/s rear that were spinning.

You say they wear out which part in my case wears and how big a job of is to replace it.
Thanks.