Yes Sir!!. That clutch got very hot! After you mentioned the high/rev clutch piston seal was damaged & fell apart when you removed the piston, you know the reason why that clutch got so hot. A slipping clutch generates an insane amount of heat very fast & with the friction material being an impregnated paper base, it's toast in seconds. If you have wondered why there are smooth frictions & frictions with a waffle or slotted pattern, the smooth frictions are fitted to the forward clutch & the waffle frictions go in the high/rev clutch. Why? Because the high/rev clutch is a so called shifting clutch & the forward clutch is permanently engaged when ever the transmission is in a forward gear. The waffle pattern helps dissipate the trans fluid quicker when the high/rev clutch releases.