Oil Burning / Valve Seals

[Rod Mathews]

My grey is burning oil eventhough it has only travelled approximately 20000 miles since it has been reconditioned. I strongly suspect it is valve seals as it does not use any oil on any long runs, but seems to when travelling around town where the motor is stopped and started regularly. It always blows smoke when it is started.  
Now if you also feel that the seals are the cause can anyone tell me how realable the "O" ring seals are. Can any other type of valve seals(ie: the cup type on Falcon motors) be fitted to a grey. If so, what would you recommend.
Thanks
Rod