The roaring sound may be the mechanical fan clutch catching due to high engine compartment heat. Mine usually comes on a short time after sitting for a while at a stop light on a hot day but stops after a few seconds of driving. The frequent clutch slave cylinder replacement is puzzling. Are they all starting to leak?? My clutch starts to behave erratically on hot days if I also have the AC on. I suspect the extra heat created by the AC condenser builds up around the clutch master cylinder and causes it to start loosing internal sealing. No problem with the brakes but the brake cylinder is metal and the clutch is plastic.