What the dealership says...
So I went back down to the dealership and asked them about the technician about what happened with the gearbox. I got pretty much the same answer as I did from the service rep; that the pin seized and as he applied leverage to remove it, the gearbox threads gave way. BUT he did produce a heat gun and tell me that he tried to heat the pin before removing it - which I think might be a bit too convenient, but there is no way that I can prove that he didn't.
One of the theories that he put forward was that the wrong type of thread locker was used when the pivot pin was put back in place, but I know that is rubbish because I used the same type of red loctite as specified in the manual. What I think happened was that he tried to loosen the pin, found it wouldn't budge, put a bit more force and *crrrack* there went the gearbox. Out came the heat gun and impact wrench and then miraculously the pin gets removed.
Let's see what I can do to sort this mess out but I can be sure of one thing: I'd rather sacrifice my own time and work on the bike myself, rather than send it in for repairs to the dealership. What a horrid experience.
Thanks all for the great advice!