I should have recognised this one
as I gave the penultimate step when solving it using symmetry on the Players' Forum.
This is a reflection about column 5 of a reduced form of the Mauricio 37 clue grid. The 5's are removed from Boxes 1,3,7 and 9.
Code:
9 . .|2 . .|. . 6
. 1 .|. 4 .|. 2 .
. . 2|. . 5|3 . .
-----+-----+-----
. . 5|4 9 1|. . 3
. 3 .|8 5 6|. 1 .
1 . .|3 7 2|5 . .
-----+-----+-----
. . 1|5 . .|4 . .
. 4 .|. 2 .|. 3 .
8 . .|. . 4|. . 7
The cool thing is Matt's use of the arrow symbols for the corners giving a clue to the transformation of digits under a 90 degree rotation that was used to solve the 37 clue version.
The cycles are {>,v,<,^} and {Green,Blue,Red,Yellow}. Grey transforms to Grey.
Numerically shifting the start point rather than relabelling the cycles are {6,7,8,9} and {1,2,3,4} with 5 transforming to itself.
Now to look for a Uniqueness trick rather than the forcing chain RW used there, and which I assume Matt has found.