2006 BMW X5 - A couple of questions

About three months ago, I purchased a 2006 X5 (4.4) from Carmax. It had $87K miles and appeared to be in good shape.

Had a few minor problems and then a big one. Kept getting an error message after which I took it to a BMW dealership who diagnosed it as needing a replacement of a transfer case. Luckily I had purchased the ext. warranty from Carmax and I had no cost impact for the fix which was estimated to be over $3K.

1) Is such a problem very common in the X5 series or for a 2006 year product ?

2) The entertainment system+navigation is quite antiquated. Are there any decent aftermarket options to replace the one (which works fine, btw) with a more modern one (preferably from BMW) ? If so what cost am I looking at ?

Thanks

Beefheart

http://www.dynavin.com/