change your gearbox oil for a fully synthetic oil and this will help.in the morning your oil is cold and therefor thick and as it warns it becomes thinner,thus seeming to get better.a fully synthetic oil is a lot thinner than the oil that is in your gearbox just now.
This is a common problem with these gearboxes. The synchro hubs go on them and it gets that bad it grinds going into gear.
1.First you will need to drain the gearbox. So you'll need a bucket.
2.Put the bucket under the gearbox.
3.With the bucket underneath drain plug, undo the drain plug with the drive of a 1/2" drive socket, i.e.
4.let all the oil spew into the bucket.
5.Now re-install the drain plug into the gearbox.
6.with your 3/8" drive socket, remove the plug which similar to the gearbox.
7.suspend the gearbox oil up high.
8.Put one end of the clear plastic tube into the gearbox oil bottle.
9.Then get back under the car and suck this end of the tube.
10.Quickly insert the bottom end of the tube into the gearbox filler hole and make sure it will stay in there.
11.just keep checking the oil level in the bottle until its emptied 2.8-3.0 litres of oil into the micra 1.3's RS5F30A gearbox.
12.When enough oil is into the gearbox, remove the clear plastic tube and re-install the filler plug!