Thanks - I've just managed to find a copy.

Looks like my fimware is 1100 as it has the visual audio fader adjustment - I don't think a further firmware upgrade is going to provide me with much I'd use so I'll probably just update the maps...although I could always get the dealer to run the firmware upgrade at some point
The only potential issue here I guess relates to warranty - would me upgrading potentially affect the warranty on the RNS510 (I have 2yrs left)?
thanks
Simon