The C6 is pretty notorious for having the clutch fluid turn black quickly when driven hard. I clean mine out every few thousand miles and if I'm ragging the car hard such as 1/4 mile runs, more frequently. This provides a great overview of the problem (watch the video) and a simple to do fluid changes.
http://www.rangeracceleration.com/Clutch_Care.html
I don't know why you get a clunk in 1st gear. It's in the clutch and not the shift itself?
http://www.rangeracceleration.com/Clutch_Care.html
I don't know why you get a clunk in 1st gear. It's in the clutch and not the shift itself?