Question from a newbie

Hi all!
Glad to be a member of this site. I've got an issue and I'm hoping someone out there can help me out.
I bought a CPO 128 convertible last year with 20K miles in mint condition. I'm lovin the car but now I've got my first issue....and just two months out of the 4 year warranty.
The issue I'm having is with the navigation. The 2008s have the mechanical version that pops up. I love the functionality and use it all of the time. About 3 weeks ago it failed to open fully...it opens proably about 75% of fully open. I can push it open and I feel no resistance but if I hit a bump it sometimes falls back to the 75% open position.
I took the care to the dealer this week and they're telling me that the entire unit must be replaced. Really? WTF?? The functionality is fine..it just doesn't fully open on it's own.
Either way..I'm very dissapointed. Either its a piss poor design-if indeed it must be replaced or BMW just doesn't want to service the car. They saw the unit itself is just over two thousand...plus labor. I guess I just continue to push it fully opened.
Can this be repairede? Does anyoe know what drives the movemet? Gears? Belt?...
Any help would be greatly appreciated.
Thanks,
Kevin