71c weird shifting issues

Hi everyone, I'm having a bit of a time with my 86na. When I bought it a couple of months ago it was stubborn going into reverse, the gears wouldn't engage and would just grind when I release the pedal. Occasionally 4th and 2nd would do the same. At other times they engage but not fully, the shifter doesn't go it's full travel but it has gear. Sometimes it shifts through all gears like butter which seems odd to me. I've changed out the gear oil for fresh 75w90 along with the clutch master and slave cylinders. The car has 212 thousand miles so it probably needs a rebuild, but I wanted to see if anyone here has some input as to what my issue is.