I swapped in a hydro clutch in my 1974 K10 a couple years back. It was a great swap! When I did the swap, the master cylinder and slave cylinder were both in 'used' condition, neither were new, but everything worked fine. Due to working conditions (and the price of gas) I don't drive the truck very frequently anymore, but when I do, I noticed something. It seems the amount of pedal 'free play' has drastically increased, meaning I can push it in a good three inches before encountering any resistance, whereas before it was only an inch or so. The fluid level in the master cylinder hasn't dropped, so it's not losing fluid. The slave cylinder is very close to the header, but there is a heat shield around the slave cylinder. My question is this: Which cylinder is probably going bad, the slave or master (they were both in used shape, no idea of mileage)? I'm guessing I should just replace them both for peace of mind, but how does one determine which is bad? Thanks Fellas!