With the talk about the heat recently, it brought memories of the time the temperature in Brisbane hit 41C and the Enfield's clutch plates got so hot that they melted together and I couldn't change gears.
I rode home by timing my arrival at stop lights and signs, so I only had to slow down a bit. I roared into the carport and switched off the engine before I hit the back wall.
I had to prise the plates apart and gave them a good wash and clean. Refilled with automatic transmission oil type F for Fords. No problems after that.