I have just had my Impreza MOT'd the tester noted that the rear wheels were very difficult to turn, possibly caused by the Rear Diff. My question is how easy should it be to rotate the rear wheels with the car out of gear and the brakes off. I have checked the oild level in the diff and it was ok, but new oil seemed like a good idea anyway. there were a few bits of metal on the Drain plug magnet but not lots.

 

Did he have all 4 wheels off the ground?

 

No only 2 wheels at a time, the fronts rotated quite easily with the backs down

 

That is why.
Jack all 4 off the ground.