What's the issue?
The other boy can do nothing about it but if I were your mate I'd say that there's been a big problem with the Astra and he's not that happy himself but it's in the garage getting sorted.
Psychologically he'll be happy to wash his hands of it then.6
Had this before with a muppet who thought a straight swap meant I'd spend the next few months fixing the issues he knew about before we swapped.
I used the line above and that was that,he was still using the car months later and sold it for a good price so the usual dreamers.