Or...just cut a motorcyle tube to size. I used that for a very long time on my Campro before my little brother replace it when he was using the car.I have been teaching some wira owner on the oil cap. Is probably the rubber gasket is old or worn. What you can do is centralized the cap then reverse lock a bit, if helps to tighten it a bit more. Try it, so far mine on the VR is ok, so are a few wira owners who did it.....