Question, i have a flat rear wheel when i pump it up i can feel and hear the air escaping around the base of the tyre valve underneath the nut. Can anyone tell me what could be the cause and the possible solution to solve the problem, for the life of me i cant find through a web search any technical drawings of tyre valves for my model of motorbike so i can have an idea of possible problem so would i need to replace the hole tyre valve or just a part, please help someone, thank you