Del Val Miata Club

This is not my car, it is a friend with a '90 but from what I have read it could happen to my '91 too. Apparently it is a well-known flaw in early cars. 

Anyway does anyone have experience doing the "field repair" involving removal of the reverse switch and poking around with a 3" screwdriver? How easy is it to do? If the owner chooses not to repair/replace the tranny, how hard is it to avoid getting into this position? The car is currently at a shop in Millington NJ, close to rt. 78. She is hoping to avoid a big expense. 

Thanks,

Gabor