Starter Motor Refurbishment (1)

[Larry 1300]

The problem that I have had with the starter on my 1.3 dolomite is that it stuck to the flywheel twice in 3 months. I freed it by turning the armature nut on the end. I decided to remove it from the car while it is laid up for winter. It is a M35J starter.
The bush at the pinion end seems to move freely when I move the pinion.
I bought another starter motor on ebay for a spare and its bush moves also.

Is it normal for the bush on the pinion end of the starter motor to move. I watched a video on You Tube and the guy says this should not be moving. He made grooves in the casing to prevent the bush moving.
(1) Should the bush be not able to move?
(2) Does the fact that it can move mean that I need to replace the bush?
(3) Should I make the grooves in the casing?
Any advice will be appreciated

[Larry 1300]

I have refurbished my M35J starter motor and put a description of what I did into the "how to fix it "sub forum. Thanks Dave Corner for your help.