Well, I plumped for the one NOT showing the internals on the basis that the seller has good feedback and on the strength of a plan to give the seller grief if it is the wrong one and claim back on Paypal. I have found it to work in the past.
I should say that over nearly eleven years with this vehicle, I have had very little trouble with this problem, but last night, I was parked twenty metres from a cellphone mast, and fiddled about for a couple of hours trying to restore normal function. Then, suddenly, it worked again and I was off. No idea why...
Again, thanks to all for your help!