GU manual gearbox cant select 1st & 2nd gears

Hello
I have been finding it difficult to select 1st & 2nd gears for a wile but thought that was normal anyway I have not driven the patrol for 8weeks jumped into it yesterday to go for a spin and noticed I couldn't select 1st 2nd gears took it for a spin around the block to try to see what was wrong and there are no strange noises just cant select 1st and 2nd gears not sure if I can access the top of the gearbox without removing it or does anyone know of a simple fix. my patrol is a 2005 ddti and has had everything repaired 12months ago for a cape trip including new engine and clutch.

Hoping its not going to be te expensive to fix

This video shows the transmission tunnel access panel removal. https://www.youtube.com/watch?v=0-jmaOZrF7Q

But to be honest, there may not be much you can do to the top unless the gear stick, or socket and bushing are worn out.

The GU workshop manual MT section has very clear exploded diagrams of the gear box components.