Seeking a Primer on Replacement Tuners

[Twincam]

The key on one of the tuners on my Squier VMJ is loose and buzzes when played. It's on the G so a rubber band stretched and doubled across them all provides a crude temporary fix; good enough for practice. I'd like to know more about replacement options from your experiences since I can only learn so much from photos at sites like guitar parts resource.

I'd like to know the perceived quality of various brands like Wilkinson, Grover, Gotoh, Hipshot, Schaller, and Sperzel.

What about ratios? I'm assuming the higher the ratio, the finer the tuning that can be achieved and the better it will stay in tune.

Sealed vs. Open?

Can a tuner be repaired on the home bench?

Thanks!