I can confirm the VW 9W7 will indeed work in pre 2008 VW's, I recently installed it (with an RNS510) into my 2005 Golf with red half height MFD.
I now have CD quality streaming, hands free phone calls, navigation etc.
Here's the break up:
RNS510 (revision F) $800 (eBay, includes 6 month warranty)
9W7 $359 (eBay, Aussie seller)
Canbus upgrade $100 (I have a spare you can have for $80)
And being genuine quality VW no hassles and everything works as it should. Well worth every cent.
I was part of a (still ongoing) forum group buy for an aftermarket RNS copy but luckily I pulled out of that, the whole thing was a debacle and didn't work out much cheaper than genuine in the end.
You get what you pay for.
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