Smoke from bonnet and smell of burning oil

[Harper]

I have a bug eye Impreza WRX from new and serviced with the main dealers. It has done 55000 miles. Recently I have noticed when I have stopped after it has been running for a while that there is a smell of burning oil and on a few occasions I have noticed blue smoke emerging from the bonnet but have not been able to trace it. Any ideas of what the cause might be would be greatly appreciated.

[D3lux]

Rocker cover gaskets.

They leak slightly on mine and the symptoms match.