CVT Transmission Problem
 

As many of you my sister R50 cooper transmission went bad. I purchased a used one from a mechanic shop. This cooper is from 2004 with 60K miles. Mechanic who it is still selling the car for parts told me that he had service the car shortly before it got totaled; and the owner ask him to sell it for parts. That transmission is also bad: jerking up when you let go the gas pedal and dowshifting to a very low gear. I tooked to a dealer to get it refresh and dealer said " the car will not reset for the transmission, which means its probably a bad transmission." My questions to all of you enthusiast is this one:
1- Do I keep investing in this cooper or move on? Car still looks great and interior is as good s new.
2- I hear is not worthy rebuilding these types of transmission. Is that right or should I have it rebuilt for a pro-shop.
3- If so, what transmission could I purchased used that will work in the R50 and it is more reliable (it needs to automatic.)

Thank you in advance for your reply