As has been said, make sure the linkage is free. I had a similar issue on my 06GSA a few years ago where the gears wouldn't engage properly sometimes and it all felt weird. It's a fairly easy thing to do and I stripped the linkage down and the ball joints were full of junk. Cleaned them up, plenty of copper grease and bingo. It should be done regularly.
I have f*cked a gearbox and believe me, it just goes bang
I have f*cked a gearbox and believe me, it just goes bang

