Turbo oil seals usually manifest themselves on lift off. When the turbo boosts, the speed of the shaft usually is enough to "re-seal" any damaged seals. Once you lift off and it starts to spin down, the oil seeps through and into the exhaust.
If it's when you're on the gas, it sounds like either excessive wear on the oil control rings on the pistons, or you're having some serious blow-by in the PCV system. Try disconnecting the oil breather pipes and put a rubber glove over the end with some rape-tape. Take it a short drive (with the gloves out the way of anything super hot) and get it up to temperature. You'll know exactly how to provoke the blue smoke so drive it as normal and keep an eye out.
The other way to check the oil seals is to whip the intercooler out and tip it up. If oil runs out, the turbo is goosed. It's perfectly normal to have a thin layer of oil all over the inside of the pipework and intercooler internals.
