Tractor hydraulic oil leaks at fittings?

My Kubota M6040 63 hp tractor I have had to re-tighten hydraulic hose connectors to stop leaks, & fear of over tighten, when trying to stop the leaks with a wrench. Is there a product you can, or should, put on the threaded fitting; or is that too dangerous because the stuff might get inside the lines and mess something up?