You won't be able to strip it without taking it off, don't know if replacing the bearings is possible. Best to just replace it. Can get them at all plumbing places. If you're fitting it yourself just drain the whole system to be on the safe side.
I'm guessing the filling loop was left open/expansion vessel flat to cause the pressure to rise and activate the safety PRV. So now you need the PRV cleaned/changed + the expansion vessel repressurising.
It would be dripping yes but sometimes it's at a rate you don't notice. The pressure not going up anymore could be the expansion vessel being flat or could possibly be a blockage. I'd start with recharging the vessel to 1 bar.
I'd start with changing the PRV and repressurising the expansion vessel, as the pressure has possibly gone above 3 bar at some point activating the valve... and once it's been opened it won't seal properly until it's been cleaned/swapped.