Just about all the outdoor fittings we use are stainless, any tape would void the mfg warranty, only liquid sealants made for hydraulic systems can be used. Leaks are 100% unacceptable and will stop operations immediately. We actually don't use much of any pipe thread for this reason, unfortunately we can't control what a mfg chooses to use in a hydro power pack. Without their consent we can't change anything for liability reasons.
I'm not saying you're wrong by any means, sure tape works. get a little piece of it stuck in valve that controls something with people on it, and someone gets hurt it's a totally different ball game.