Despairing of having the machine repaired or replaced I dismantled it to see what the problem was. The little plastic post supporting a small pinion had broken off. I repaired it with a brass pin reduced and screwed through the front panel and held by a nut. (A pin from an old UK MK 2A 3 pin lighting plug supplied the part - just happened to be .002" smaller in dia
)
I didn't think that the internal mechanism was robust enough for the job; especially in plastic.
Although the spec was for an O2 Xda IIi which has a 2.5mm audio socket, the audio jack on the Arkon was 3.5mm and I had to buy an adapter. The support jaws, although lined with rubber, did not provide a positive grip and the PDA tended to fall out. I used a Stanley knife (box cutter) to gently remove some of the rubber padding leaving ridges vertically along the front to positively hold the PDA.
There is an irritating feedback to callers from the mobile telephone function so, for the car, I've gone back to using the old Nokia 6310i, with a pay & go SIM, in its carkit.