So my questions are where is the best place to buy? Are the ones from Europe dodgy or fake? I've seen a couple of versions of the RNS 510 - which one do I need for the MK6 GTD?
I got one off eBay from Lithuania for £510 including delivery. It is practically immaculate. You'll notice that the majority of the Lithuanian / Polish sellers have 100% positive feedback over 100's of transactions and all they sell are Sat Nav units! Whether they're actually from write off's (like they say) or stolen is questionable - but they work well and usually come with a money back / replacement guarantee.
There are a couple of companies on eBay selling brand new units - but then they charge a premium £1000 price tag to go with them!
There are 3 versions around at the moment - A, B and C. The C versions are the newest, but they are basically all the same in terms of hardware and looks. I got an A version, and updated the firmware (pop in a disk and leave it for 45 mins) and its effectively a C version now.
All versions will fit in your GTD. You'll have to update the firmware to the latest if you want it to work properly though with the climate control display coming up on the SatNav. I
think the firmware on a C version might already be up-to-date enough to do this... but C versions are pretty rare on eBay at the moment.