Nissan Maxima rattling under load

The CVT in my 2008 Nissan Maxima is "rattling" under load and sticking in a low gear down hills causing it to over-rev. I have discovered the CVT is a problem in Nissans here and in the USA where Nissan USA doubled their warranty to six years and 160,000 km. I am now up for $3500 for second-hand replacement. The dealer I bought it from and where I have had it serviced car is being evasive and will not discuss why a 140,000 km five- year-old car has a main drivetrain component that's practically unserviceable. Is this common with CVTs over 100,000 km?