Ugly noise
 

I have a 1998 Boxster with 95K miles, it makes a horrible clanking noise coming from the passenger rear wheel only when I make sharp left turns at a relatively fast speed. My local mechanic (not a Porsche specialist) determined that my transmission / axle needs to be replace at a 4500.00 dlls. rebuilt transmission from the factory plus 7 hours of labor. Any ideas or suggestions?

I can understand comments about the suspension / rear axle related parts, but not transmission.
Anywhooo... I would ask an independent Porsche specialist or two, and look at the car with them while it is up on a rack. Ask questions. And don't mention what someone else said.

Take it to a Porsche Dealer Mechanic, so long as the suspension is stock and not modified, they will go on a road test drive and suggest what they suspect is wrong for free.