I have a ball valve on my catch cans too (got 2 cans) and they never leak like that. I would be quite suspicious about the seal in the ball valve failing from oil/gas deteriorating it or just a poor valve design. You can check if the valve is failing to seal fully by taking it off and blowing...
Just saw this post now, but I've been running the Supertech 88mm pistons. I have a few track days and lots of daily driving on the rebuild. I think right now I've got about 63k KM's on the rebuild engine and compression appears to still be 185 PSI across the board.