Bevel Drive and Rear Viscous Coupling

My Volvo broke down a couple weeks ago and the dealership said that I need a new Bevel Drive ($2500); I got it back from the dealership and it worked great for two days before breaking down again; this time the dealership is saying it’s the Rear Viscus Coupling, another $2500. Has anyone heard of these two going out at the same time, could the dealership have mis-diagnosed the problem or cause the Viscus Coupling to go out? Any thoughts out there,I just also got the timing belt replaced and could now be into a car for 6k that is worth half of that.