There aren’t many parts left on the Mini that haven’t been replaced or refurbished, but it seems like those are the pieces that are failing. Like the starter motor bendix gear, which, despite being spotlessly clean when installed, refused to engage in a busy carpark.
So now we have a new one. They’re easy to install. Place starter in a vice:
Hold the bendix gear in the engaged position using the correct service tool (or masking tape):
Then all you have to do is compress the bizarrely strong buffer spring using the correct service tool (or a couple of vise-grips) so you can remove the spring clip:
Reassembly is the reverse of removal, except for the bleeding.