There is a growing trend for the TRX300 Honda utility machines to
develop a sudden oil leak on the upper part of the right clutch cover. When this happens it usually manifests itself towards the back of the cover in the vicinity of the kickstart shaft. What is so unusual is the leak tends to occur in machines that have never had their covers off since it was put on at the factory. There is no damage to the case or the gasket surface. It just starts oozing oil. Upon clutch cover removal, something unexpected is found. The gasket has become hard and brittle, and has lost adhesion with the cover and was sucked downward, allowing oil to escape through the now open slot. Note how even the gasket bolt hole is even elongated.
Apparently because the cover mating surface is quite thin at that point, when the gasket becomes hard with age, it is susceptible to being pulled downward. When that gasket is scraped off and replaced with a fresh new pliable gasket, the leak is stopped.