At the base of the gearstick is the nylon baseplate that locates and holds the gearstick in the gearbox. The red circle shows the side face of this plate and the blue circle shows the metal lug on the gearstick that rests on this plate when selecting 1st gear.

This is also the lockout for reverse and when you push down on the gearstick you slide under this nylon baseplate and select reverse. Over time as the metal rubs against the nylon it wears and the wear face is shown circled in red below.

This causes vagueness in the 1st/reverse selection and, in extreme cases, the reverse lockout no longer works. The good news is the baseplate is easy to replace and this can be with the gearbox in situ.
There is also a nylon bush at the base of the gearstick (below) and I would suggest replacing this whilst it's all apart.

Our other NC tips and tricks can be found here - http://www.mx5parts.com.au/category/tips-and-tricks
Chris
mx5parts.com.au