Slipping out of gear every time in 3rd gear

Hi,

I recently had an issue with my gearbox on my Vauxhall Astra, as I understand it it is quite a common issue with the M32 gearbox in that the bearing on the 6th gear quite often fails. This occurred to us and we put the car in to the garage. The garage stripped down the gearbox, checked over the gearbox components and on that basis, recommended that we replace the bearings, replace the dual mass flywheel, concentric slave and also the clutch. This was done on the basis that there was no further damage to any of the gears themselves.

Around 6 weeks later, I noticed that the car occasionally slipped out of 3rd gear. A week or so on and we can no longer use 3rd gear as it slips out straight away and sounds as if it is clattering the gear. If the gear lever is held in place, you can come off the clutch but as soon as you let go of the gear stick then it slips and clatters.

My question is twofold.

1. Presumably the 3rd gear will need replaced? What sort of costs (part wise & labour time) would be involved here?
2. In your opinion, do you think I have a case to put to the garage which did the original repair in the sense that there must have either been damage to the gear or it may not have been put back together completely correctly? I find it hard to believe it is a completely unrelated issue. Having spoken to another mechanic, he mentioned he would imagine it was due to a mechanic error in putting it back together.

I spent £1900 'fixing' the gearbox previously, it's almost not worth fixing the car if it is going to cost me too much more. In my eyes, we followed the garage's recommendation and the work was insufficient to resolve the issues that we had at the time.

Thanks for your help and advice!
Regards,
Pete