What many months ago seems from the driver seat to be a bad tire noise that amplified since than is in fact a noise source coming from the final drive (differential).

After eliminating the tires, the wheels bearing and the rear disc protectors touching the discs as possible cause i than suspect drive shaft bearing (the central one) so we raised the car on the lift yesterday and run it at about 75 mph (80 km) in third speed, from under the car moving front to rear and listening with a long screw driver from place to place it was obvious that the hissing / groaning noise source was the final drive and

I am glad because we finally pin point the noise source, but i am afraid of what the solution could be and could cost !

Following this test on the lift it's difficult to say what within the final drive could be generate the noise (main central gear bearing ? Else ?). The picth of the noise is directly proportional to the speed of the car, no noise change for exemple if i put the foot on the clutch when driving, neither when i accelerate or decelarate abruptly.

The three oil seals of the final drive was replace by the dealer at 265000 km 2 years ago the car as now 289000 km. The final drive start to leaks a bit few months before but the final drive oil level was always fine (never miss oil)

What's your experience ? your comments ?

Is it possible to rebuild the final drive ? or will i have to replace it by a used one ? Cost order

My 535 is a manual one i don't know what is it's ratio used one could be rare, could 535 automatic or 525 final drive be an alternative ?