E320 Valve Cover oil leak and front boot worn out
 

I have a 1999 E320 Wagon. I noticed some oil spots in the garage so I took it into my local mechanic to have it looked at. When he put it up on the lift he determined that it was leaking from the Valve Covers. He also noticed that the boot on the drvers side axle was worn as well. He summized that I should replace the axle verses just the boot as that is the procedure that is best to do. His total estimate of changing Valve Cover gaskets and replacing the axle with the boot would be $700. I have used this mechanic solely for all my vehicles over many years, however, he does not work on Mercedes regularly, but rather gets his information from very close associates, who are indeed Mercedes experts, so to speak. Does this price seem correct for the work, labor and parts, to be done, and is changing the axle the right thing to do under the circumstances? Thanks guys.