You're better off checking www.e90post.com/forums
for more information. Many more active E9x users on there. My father has an 07 335i vert with no problems on the hardtop yet. During pressurized car washes (which the manual prohibits you from using) there can be some small drip on the front windows where the roof latches meet the A-pillar locks.
As for the extended warranty, I can't help ya there. Perhaps give the dealer a call and inquire if it's current lease is through BMW Financial, would it be eligible for extended warranty coverage?