Its a shame you crashed it. I understand that was traumatic, but you have no chance of selling it at that price without pics.
Face the fact, you are going to be reminded of the crash heaps of times. You can't ignore it.
Mahle pistons due to their composition for street use. But really what are your plans?
There are heaps of examples of stock pistons being perfectly suitable for big power.
Did they make changes to the tune so it would rev cleanly?
Anyway, as mentioned I would hope they drive it in the road to confirm the issue is gone.
Would be nice to see a dyno printout with the Afr shown.
Can't wait for it to be all sorted !
Oil is pretty normal to build up in tubing and intercoolers, but hard to say how much you are referring to. If its not pooling up and is just on the walls don't worry.
Vac leak would make it run lean when off boost if the leak is in the inlet manifold . rich if its a boost leak in a cooler pipe.
Did it always do it@
You should really take it somewhere and run it on a Dyno to check it out.