adz beeh

Hi guys, since the winter has come round my DTR doesnt like starting one bit. At first i thought the cold weather may be the problem, but now im starting to think there is a fault with it as i have lost quite a bit of compression. You can kick the bike over as many times as u want but nothing (sometimes u may be lucky n it will start). The bike will start if i bump it and will ride normally. It will also kick over once the bike is warm. Is it a seal??? if so which one??? Any advice or feedback is much appreciated many thanks Adam