If you use a washable cotton gauze filter, like a K & N, be aware that all of the other filter manufacturers, and there are a lot, sell the same 'cleaning kit'. AFE has the least expensive, and offers different colored oil.
The cleaning kits are only about $12 retail, and they come with oil and cleaner. It's really not that much money, considering how many times you can use them.
And I agree, though, about over-oiling. Most people do, and that's a bad thing.
I use a K & N, with an Outerwear sock. With the Weber, you don't have a lot of alternatives, as the 'stock air cleaner' adaptor is really a pile of crap.