Slave cylinder problems are always related to high pedal effort. High pedal effort is due to the throw out bearing galling on the input shaft sleeve. It's not well known, but you really need to pull your TOB fork periodically, and get your hand in there with a rag and wipe all the old dirty grease off, and re-apply new. Also inspect the fork for wear. The TOB contact surface should be very small. If the fork has a worn flat spot on it, then it is time to replace the fork.