need help

hi lads and lasses, i have a 2.7tdv6 that blows white smoke only once the engine is warm. Was told possibly a piston ring??! Really hoping its not. It runs ok, a little off but not drastic. loss of power and after having a poke about the egrs havd been blanked off before i bought it, the other thing is the glow plugs are pretty shot so could this cause an issue.. Really could do with advice, im not sure where to start with it

You want to put a diagnostic on it. It's a computer controlled engine, so you'll get loads of information by looking at various readings.

I'd be looking at injector balance, as this will tell you if an injector is out of specification.
Also the MAF, MAP and fuel rail presssure will be useful too.