I would never argue with someone that wanted to replace all the stuff while he was THERE..... The most likely leak is the Turbo return tube ,,, they are famous for leaking....

On the section about the turbo charger replacement it (FSM) says,,,, install in reverse order..... "please note the following points:

15 Prior to installing turbocharger, attach adapter fitting and oil return pipe. Correct positioning is absolutely essential. "

The Haynes manual does not indicate any differently...

Neither , of course, address specifically trying to replace those seals due to leaking....

So my conclusion is that you need to take the Turbo off to properly replace that gasket, and three seals.... Sorry,, it could have been made so it could be done otherwise.. Greg