there are no "seals" in a turbo (except draw thru turbo's, different story there, but only on the compressor side, and only to deal with high vacuum). If you have oil pushing into the turbo through the oil return line, even on a brand spanking new, perfect condition turbo, it will pour out of the center section. Same goes if your return line is too restrictive, causing pressure to build in the return line.
Here's a simple test, so we can narrow down the problem. With oil in the motor, pop off the return line at the turbo and hold it at the same level where it attaches on the turbo. If oil comes out of the line, then your oil level in the engine is higher than that point and nothing you do to it will fix it (other than raising the turbo or lowering the oil level or install an oil scavenge pump/system)
If oil DOESN'T come out, slowly lower the hose and see at what point the oil comes out. Optimally, you would prefer it to be at no point oil comes out of the line (oil level is below the return line fitting on the motor) But its not absolutely necessary....but the lower it is, the better.
So assuming you've passed the test up to this point, you still have too restrictive of a return line. Go with bigger lines, bigger fittings and less complexity.
As I mentioned before, turbo's are VERY sensitive about the oil return line. its very crucial to design it well....my first turbo system I made, I did the same thing, and you wouldn't believe the clouds of smoke I created, while testing different strategies with the return line....that system was mounted too low and I had to make a scavenge system which took quite a bit of trial and error....but I did eventually get it to work well. But its a last resort. If you can get gravity drain to work well, its definitely the way to go.
<!--EDIT|Uncle Bob
Reason for Edit: None given...|1102420246 -->
