Holy sh!t, man...that's HORRIBLE.
You know, I'd fight that crap right down to the end.
You sent back a product, expecting it to be replaced under warranty. You were not told they were going to send you a new one in place of the old one as you DID NOT ASK FOR A NEW ONE IN PLACE OF THE OLD ONE IF THE OLD ONE COULD NOT BE REPLACED...(or did you?)
So I'd tell them to take that 25% restocking (rip off) fee and tell them to shove it up their ASS. YOU are the one with the credit card and YOU are the one either allowing or disallowing the charges. YOU call the bank if you did not authorize the charges for a brand new clutch, restocking fee, etc.
Tell them you will pay for the shipping of the old clutch back...nothing more, nothing less.
If they refuse, call the bank. Deny the charges. Then file a complaint on them with the BBB. One complaint won't change the world, but as they begin to tally up, stuff happens...kind of like a little old shop in Dallas.