The Shodan filter reference only shows a way to search using the hash of all the HTTP headers (http.headers_hash) in a banner. Is there some way to search for specific header fields or values?
You can just search for them directly as they're contained in the main data property of the banner. You don't need to use search filters. For example: https://www.shodan.io/search?query=%22X-Recruiting%3A%22