Anyone ever had their transmission jerking/shaking when turning?

Hey everyone,

I have a 2011 impreza wrx, I've been having an issue with car shaking or jerking when making sharp turns. Anyone ever experienced anything like that?

Took it to a mechanic, said the suspension and steering components are fine, that it looks like the transfer case in the transmission seized up.

He recommended flushing the fluid to see if it fixes itself on its own. And if it doesn't, I might need new transmission or rebuild.

I've had it flushed, some treat added with new fluid as well, and so far nothing.

Anyone ever had this issue? Any other tricks that can be done to unseize it? Or maybe mechanic missed something, the gears shift fine, no issues there.