No need coating the expansion plug, would do no good if it was leaking.
The fitting at the hydro unit is a *37 flair fitting just like any hyd fitting, that is the one you want to separate.
also loosen the other fitting (at the rear casting) to give looseness so you don't have to bend the tube.
and Sorner has you covered if you needed to replace the expansion plug but I think they are still available.
