IIRC, transmission fluid should be changed every 30,000 miles.
Also (not sure on this) the early B16 transmission (cable) have single synchros, the later have double on certain gears.
D-series CRX transmission have no synchro on the reverse gear.
A heavier shift knob can sometimes smooth out shifting.
And a short shifter can increase wear on the synchors.
Jamming it into gear too fast will cause excess wear and grinds as well.