Maybe a 5. There is nothing hard about it, but it takes some time. Removing the manifolds and replacing them takes maybe an hour or a little more the first time. Scrubbing and wiping the crud off is a long process, and a pain, but not really tricky at all. Just take your time, read a lot first, and follow the tips: get TONS of cheapo Wal-Mart cleaner, and let the cleaner do the work.
