Mission 29 - Confront Andy Turetto
This takes place in the same compound as the first trailer burn in Sabotage the Union Trailers, and the plan of attack is much the same. (If you didn't perform that mission, follow the link both for some further pointers, and the location of the Vargas painting on site.)
As before, the side door gives you a slightly stronger advantage than the sewers, and you can kill a troublesome pair of guards immediately. Added bonus- this time there's not even a guard on the gate.
As before, ascend to the office, whistle-killing as you go, descend, and take out the sentry in the garage. Double back and take out the sentry in the trailer, then check out the sniper perch again. No sniper today, but his rifle is still here, if you want to cap that last sentry the easy way.
There's also a another Manitou lying atop a crate on the far right walkway if you need more bullets.
When the smoke clears, Turetto should be the last enemy alive. Sneak over to his office and he'll probably still be peeking out the far window. Take him in hand and recruit him over to your side.