Electronic Gurus: RNS510 Issues

So I bought a used RNS510 and an OEM Navi upgrade DVD.
First 510 kept saying error check DVD/CD. But it would play audio CDs just fine. Same thing with retail bought movie DVD, errors out after a few seconds.
The source I got them from sent me THREE replacements and they ALL have the same problem
I used one of those "CD cleaner discs" with the brushes on it on one unit with no change.
How can I have FOUR RNS510 with dead DVD drives? The ones I have are original and first revisions. I borrowed a friend's "E" version and a movie booted right up and the map DVD was recognized instantly.
Is it worth opening these units up for further investigation? What would I look for?
Thanks

If I'm not mistaken, rns and rcd stereo change requires vcds coding.

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Yes I use VCDS to set the audio system as my car has Dynaudio.