Wow. there is a lot of great info on this thread...  I bought a 2013 coupe new and the only fluids that I changed were the motor oil.  I think that unless you have mechanical issues with drivetrain or with leaks then I would just follow the owner's manual recommendations exactly. I should also mention that I park my C6 over the winter and just do an oil change before storing it no matter what the mileage is...  I also plan on doing an oil analysis when I change the oil this fall.