It sounds like it might be a little messy and therefore the manual intervention. It's big $$, so they don't want to make a mistake. There are entire teams dedicated to Manual Intervention and you have to have lots of FAO experience to be in one, so at least you know it will be done properly.

It might be worth ringing to ask how long it might take, I'm not sure if there is a 'time limit' on man interventions.