I would go for the Z4sDrive 35i, given that it has the hard top convertible. Whilst the Z4m is a good car it seems that some of your failures are more about age than mileage. Plus peace of mind of the extended warranty, the only other consideration is cost, either part ex or sell your car privately and go for a cash type deal, this is a decision for yourself, look at trade in prices or how much your model and year are going for privately, are they selling??? Pointless selling privately if you cannot sell it........
There have been some issues with the Z4sDrive35i, you can read about them on the forums, at the mileage on the potential new they have probably been ironed out, but you can still check before you buy, having said this a 6 year extended mileage (provided it gives you the cover you require, not all warranties are the same) should give you again peace of mind!!!
Always said I would go back to a 6 series
Last edited by 645/333; 03-24-2014 at 06:49 AM.