Your next move would be to visually inspect the turbines ring lands to see if you can detect any wear. If your car is already smoking and you don't have much oil slime on the compressor side, there is a good hance that your oil seal and probably your turbine is shot.
Here is my old 145K turbine, I took out the center cartridge but left everything intact when I built my first T Bird. I used this center section as a back up in case anything happened to my T Bird. I'm lucky I kept it because the T Bird lasted only a couple months and a dyno session before I had to swap my old one back in. My 145K turbo lasted almost another year untill it blew on the way to a meet in Lake Elsinore. Anyways:
Doesn't look too bad right?
Look furthest left before you get to the turbine, that little notch isn't supposed to be there, it's where the oil seal wore against the ring land
Here is a better picture of what I mean:
See that second line, the one I drew the arrow to?
Well the oil seal sits in that crevice but shouldn't touch the sides when the turbine spins. It's meant to hold oil back not spin with the turbine. The oil seal itself is quite larger than the actual ring land/shaft that it sits in:
Here is the best picture for an example:
Here you can clearly see how it wears and allows oil to slip past. The oil seal is allowed to wobble all over the place instead of staying stationary within the confines it is supposed to.
Here is the back side of the oil seal that belongs to this turbine:
Now here is the side that wore against the backside of the turbine:
That isn't solely carbon build up on the outer edges, it actually concave from wear
Here is a better picture of it:
Notice how is is larger than where it sits. This is to allow you to move the oil seal over the first and second section without distorting the seal:
A better picture of how it sits:
Not entirely, I left part of it out so you can see the wear ^
Here is how it actually sits:
Notice how much tolerance there is between where it's supposed to sit and where it actually can be moved. With a good turbine and a new oil seal, it is a tight fit with very little tolerance for movement.
So, what have we learned?
1) If your car is already smoking, you have good compression, your oil seals in the head are good, then you're going to be breaking apart the turbo.
2) If it's already smoking anyways, you're going to need to break it apart regardless if you want to or not. Or buy another turbo, that might smoke in a month or so. In this case, good luck getting your money back for a used item.
3) Get all of your parts before you start. If you're anticipating your turbine to be in good condition, be prepared for it not to be.
4) If you're planning on doing just a basic job, be prepared for basic results.
5) it can be done provided that all parts are in good working condition
6) Don't be scared, it isn't as hard as it looks.
7) Just do it
8) You'll be glad you did.
9) I deserve karma
10) I deserve karma
Alright enough numbers
Seriously though. If you've gotten this far, you either care enough about your car or want to learn something new, hopefully both. If you aren't planning on going to full rebuild route, order the two oil seals that go on the piston on the compressor side and the oil seal on the turbine, cross your fingers, and hope for the best.
Good Luck and Happy Boosting!