They are a ba$tard! Its all to do with the self adjusting mechanism not being fine enough and the adjusting springs inside being damaged. For a road car they must be a nightmare.... for a race car they are OK so long as you re-adjust them carefully after every track session! We looked into doing reconditioned on an exhange basis, but its not really viable as soem of the opnes coming back to us were really unrepairable and with a complete lack of spares the project never really got off the ground.
Now we are looking at modifying the mechanisms to conatin a different sort of self adjusting, non return system based on clock mechanisms but its really early days.....
I remember after every track session feeling each wheel with the back of my hand. When the rear wheels were cold, I knew it was time for a quickie brake adjustment!
Still, when properly adjusted, it's the best handbrake there is, as they directly grip the rotor.
I also enjoyed showing other vintage racers the rear dunlops, which always made their eyes bug out, especially after I passed them.