You are both gentlemen and scholars (thanks)! Dumb question (another one): when I took the high-side hose and fitting off the compressor there wasn't a true o-ring there (it wasn't rubber). It was more like a plastic spacer of some sort (I'd attach a picture but it is just the black ring
). Is this the only thing I should be replacing or should there be an o-ring at this location in tandem with the plastic spacer ring?