if tranny is otherwise working well i wouldnt risk replacing it. the center diff can be removed in the car.

in a FWD car when you turn the outside wheel has to travel a greater distance. thats what the differential is there for. to allow the inside tire to turn slower and the outer faster. when the diff is welded its a nightmare to make a u turn. the inside tire has to turn backwards while the outer turns faster. very hard on the tires. they literally scrub to death during turns.

the front and back wheels of AWD car act like the left and right wheel of FWD. and the center diff is like the diff in FWD. when front tires are turning faster the rear have to go faster than the pavement to catch up. so they are screeching across the pavement. this is very hard on the drivetrain. especially rear diff which will chatter and heat up quickly.

the car had a what sounded like a dragging rear rotor from sticking break caliper or possible a worn bearing. both of which would have masked any other sound the car may have been making. hope you get it worked out with too much pain..