Reverse gear issues Vectra c dti 1.9?

Occasionally my vectra won't go in reverse gear. No noise, just a physical refusal to slide in. It goes in second or third time after double clutching and some welly, then is fine for up to a few weeks.

She's very jerky off the clutch into second gear, and sometimes grinds so I have to re-insert into second gear.

I've not taken her to the garage yet, just wanted some advice to see if there is any chance in hell her 80,000 mile gearbox isn't wazzocked. 2006 model and 80,000 miles seems a little premature for gearbox failure.