Gear grind selecting into reverse (2011 GU CRD manual)

Just bought a 2011 GU VII manual 5 speed, good service history at ~170,000kms.
Issue occurred when I wanted to reverse into a parking spot. The car was still inching forward but very very slow, clutch in, gear selected reverse and that's when the grind happened.
Next time I parked I was braked fully and was stationary for 1 second before selecting reverse, still grinded.
Now I wait a few seconds when stationary before going into reverse and it's been okay.
I've owned other manual cars that allow me to gear select into reverse whilst still rolling forward, is this normal?

Maybe bleed the clutch fluid at the slave cylinder.

if the clutch is okay it maybe a gearbox oil problem . either low or old oil or it maybe the wrong oil . the patrols need a gl4 specification oil but some put in gl5 oil without realising it because it is more common and it causes difficulty changing gears .