I am the third owner of a 2014 818. The donor is a 2002 WRX with ~132K miles.
Most of the rework and assembly was done by owner #1 and I have never had a link to him.
It has always been a hassle pushing the chassis as there is a substantial amount of drag. I assumed it was (Wilwood) brake drag on the rear axle.
Today I said "enough" and pulled the rear calipers; that changed nothing, so the drag is in the transaxle.
Either left or right (apparently no traction lock) will resist, then turn with effort. There is a slight hissing noise as the wheel/axle turns.
With no experience in this assembly my intuition is the drag is not normal. OTOH I expect only the differential and main shaft are turning.
I assume the 2WD rework does not require a change to the ring/pinion, so unusual gear preload should not have happened.
Let me know if this condition is typical, or what problem may have been induced during rework.
jim