I currently own 3 machines for sure with nylon gears. 2 of them are broken. The gears aren't expensive and will probably be good for another 40 years when they're replaced. I just need to get the nerve and time together to tackle them. My biggest hurdle is I tend to gravitate toward the older black single stitchers and I have a line of them that are getting all my attention at the moment.
The plastic gears are a consideration but if the machine is worth it I wouldn't let it stop me. Your Bernina is one of the few vintage machines that fall into the "worth it" category financially if you have to pay for the work. My machines are only worth it because I like them and will do the work myself. I haven't dug that far into any of my machines yet so I'm hoping they will be a good learning experience.
Rodney