I admire your confidence. Just a day so they can replicate the fault, then maybe a week while the gearbox is stripped, repaired and rebuilt by an unknown quantity, then the doubt as to whether this is really a proper fix. In the meantime, without your car and sat in a courtesy car if you're lucky.It wouldnt do any harm to take it in for them to have a look at the very least.
I think I'll wait for more information.