99.9% certain it's manifold bolts. If this is a reputable dealer they should own up and fix it. Cost to repair will be somewhere around $1000. Depends how long they have to work at getting the existing bolts off. They remove the front wheel and fender liner and go at it from there.
My 2008 had to have both sides done over a two year period. Both under warranty as they are under the 5/60 power train warranty.
And NO, you didn't make a bad choice. You will be extremely pleased towing with the V10. Not too many people buy a used vehicle and not go back for a few items to be repaired.
S
