Been driving my little 1950 Land Rover around . The locals stare at it or me , not sure why ! It has a 1954 engine and 56 transmission. 
A strange ongoing mechanical issue came up , go for a drive and from the start the gearbox and clutch behaved normally , after 10 mins on a bitumen road strange things , gear selection not easy , very crunchy and sometimes gears refused to mesh. First gear impossible to select.  Whats going on, behaves with no problems when cold but after a drive it all jams up . Checked oil levels , adjusted the clutch linkages , still have the problem.    
 
Then a hammer hit me, after a drive on a dirt road , the problem goes away . I discovered the answer. 
Anybody have the answer ? Quiz time .