'83 gti sunroof rear height adjustment

The two rear height adjusters for the sunroof lost an essential part when I was adjusting - the small internal collar that allows the mechanism to rotate perished so now I either have to make do with the correct adjustment height and that mechanism unable to rotate the 75 degrees or so which means the sunroof doesn't lower enough to be retracted - will scratch. Or I have the screw adjustment too loose which allows the sunroof to drop but then won't return to the correct height when closed as it's dropped on the teethed height part. 


Any idea where I can get the replacement collars that are obviously needed?