105,000 Mile Service

I had my 1992 500SL into the dealer today for the 105,000 mile service.

Two problems I knew that I had. First, the blower on the climate control system has quit. The tech's suggestion was to special order a $500 blower regulator, install it and see if that cures the problem. Here is my first question: isn't there a way to check the regulator before ordering and installing? He says no.

The second problem that I knew of was an underbody rattling sound that just seemed like something was loose. The tech said: strut bushings. Replace for $500.

Then there were two problems that I was not aware of. First, I need a belt tensioner to cure a high pitched whine that is noticeable when the transmission shifts gears. $500 plus labor. Second, I need new rotors on all four wheels. (The brake pad dash light has been flashing for about a week.) Roughly $1,000 plus labor. I have replaced these before, but cannot remember when. What is the reasonable life on rotors?

I have no reason to doubt the dealers honesty, but does this sound reasonable?
Thanks, JR