Shortly after I'd bought my Amazon I had the same problem for a few weeks. Then it largely disappeared, although it was never again easy to select first gear from standstill, especially with a cold gearbox. I drove like that for more than two years.

This year I rebuilt a M40 and swapped it for the tired one. I opened the old 'box and found that one of the detents was chipped. That's probably what had caused the difficulty with selecting first gear. Though worn a bit, the synchromesh ring wasn't too bad.