[Aussie Mike]

The T56 has carbon synchro rings for all the forward gears but reverse is a brass synchro ring for some reason. I have often heard of them having troubles getting into reverse.

A few of the used T56 boxes I've stripped and built have had quite worn teeth (maybe dogs is the right term) on the section that engages with the synchro hub. Fortunately reverse gear has these teeth on both sides of the gear and only one side is used. You can pull reverse gear out and flip it over and use the fresh set of dogs. To do this you only need to strip off the extension housing.

Cheers