The pins are in the sleeve right behind the main body of the transmission, in front of the od unit. They are accessible on the M45 and 47, but on an M46 the gearbox has to come out. I don't think there is much a person can do to avoid them wearing, but adjusting the reverse lockout plate solves the worst part of the problem. Eventually they wear to the point that it is really tough to shift, but most people wear the clutch out before that point, giving you an opportunity to make the repair. The sleeve is hard as a stone and seldom wears, the pins wear most, and the shift rods themselves wear some too. Most of the time, 2 new pins brings it back to an acceptible level. You should also check the pin and bushings right at the base of the shifter- They are easily changed and contribute to sloppy shifting as well.