Using PH0 Screwdriver remove the 4 screws attaching the mount ring to the lens.

There is a small amount of threadlock on these screws.

Screws: 4@ M1.6 x 6 (white threadlock)

Carefully lift the mount ring. The lens sealing gasket may have adhered to it and lift as well. This is ok.

Remove the lens sealing gasket, and two metal shims.

Note the profile on the gasket. The longer bevelled edge faces outwards.

The metal shims are identical so can be replaced in any order.

Note the plastic pillars to align the parts.