Hello, I lost the rubber gasket that seals the water filling cap. I'd like to purchase a replacement. How can I do that? The unit works great. Another question is how should I clean the air filter. It is looking a bit clogged and have vacuumed it at full strength. I tried removing the 5 obvious screws at the bottom of the case but was unable to separate the two halves. I suspect some additional screws that are hidden.