We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "Forestfan"
saying something like:

Apologies for the poor mobile phone pic, but how do I remove this little
beauty?

http://www.forgemill.co.uk/mira.jpg

I can see a few openings for what appears to be a 2.5mm allen key (missing
from my set), and the nuts at the back on the inlets.

Pull the central knob straight off - it's on a four-grooved shaft, iirc.
The rotary outside one also pulls straight off after that once you
remove a horseshoe clip.
The 2.5mm allan grubscrews round the periphery will allow you to take
the body away from the backplate once removed.

Is it knackered? You can get a complete rebuild kit for about a tenner.

--

Dave