You don't have to reoil the filter unless you clean it. You shouldn't have to clean it for at least 10K. Remember when you oil it, it only needs a VERY light misting. After the first drive around the block, clean off your MAFS, since oil will collect on it after the filter's first use.
1. K&N filter cleaning kit oil.
2. Any auto store should have it.
3. Spray it down from the outside with the cleaner, let it soak for a few min, rinse it out from the inside with cold water only, let air dry.
4. Spray it with non-chlorinated brake cleaner.