Recently installed a Goodwin Clutch kit in my 2005 Mach Z. Performance improvements are very noticeable over a stock sled. Good investment for the money with the Goodwin kit.
HOWEVER- You must use the stock factory set screws to hold the weight pins in place. If you use the carter keys supplied in the kit, and install them with the heads out it will break off the head of the carter key. This is more of a problem when you set the clickers down to #2 or below as the ramp get closer to the clutch.
Mine was not back shifting right, and every once in a while would shift irradically. Opened it up and found 2 of the 3 carter keys broke and gone. Weight pins were shifted as far out as they could slide.
The kit includes carter keys for the weight pins, but does not specify to use the stock factory set screws in the instructions.
No damage to the clutch was done with this problem.
The Goodwin clutch kit works great, and is priced very competitive as well.