Aside from fluid (which has been covered very thoroughly by the other posts), have you adjusted your reverse lockout plate? The M47 is funny about going into first gear sometimes, and often is because of the lockout plate being out of adjustment. It is right beneath the rubber shift lever boot, and a very small (like 4mm) socket will adjust it. Or you can play around and try to shift into first while pulling up on the reverse ring on the lever (careful with that).

Also if your shift bushings are shot they'll cause trick shifting too. But more likely just either the transmission or the reverse lockout plate.

Additionally, sometimes a really tough-to-shift trans is because of a dragging clutch, even if just very slightly. My 91 has several of the above problems :)