[Sunfish (Ray)]

Perhaps it is the front cover that rotates. The secondary housing should not rotate and is fixed in most cases to the corrector.

The corrector must go back exactly as set up in the factory with its serial number and makers mark pointing to the three o clock screw with the same cork spacers in each position. The corrector is not perfectly cut round and centred in all cases and so the spacers are not equal.

The secondary often has a makers mark also , sometimes visible through the cover which also points horizontally to the three o’clock position and the whole assembly is matched and tested on the bench at manufacture, with matching numbers on corrector , secondary and mirror.

Anything else will not provide the best possible result and may be difficult to collimate.