:thumbsup:
I had the thought going through my head that your couplings were of the push/pull vintage.
Glad that you had the expert advise to get it figured out.
One reason I believe they were used, was with breakaway equipment that allowed for the hyd. hoses to disconnect without operator help, thus to avoid pulling a hose apart and have oil spraying all over.
Keep the area clean of dirt so it doesn't get into your hyd. system. The caps help that, but are not the complete answer.