Unfortunately, this is quite a common problem with postwar Douglases. The ideal repair would be to replace both the thrust ring and the clutch cam (as these both incorporate the bearing tracks) but they are becoming scarce. When you get your clutch release out, if it's not too bad, you may find that it can be reclaimed by having the tracks reground to suit 1/4" balls (7/32" was standard). When reassembled, adjust the cable so that there is some free play on the operating arm - if the thrust bearing is under constant load, it will soon start screaming at you again.
Regards,
Eddie.