Anyone stripped it down fully?
Yes I have. It is an arse. So much so that I started a thread on here about it.
BTW do not believe the suggestions that you can remove the hood covers without disconnecting the cables and hoses. You can on other shifters, but not the Rival Hydro R.
Can you get all the replacement parts?
No you cannot. Nor can you get just the shifter, they’re only sold as complete units (shifter, cable inner, hose and brake) and apparently only ever were.
However, often it’s that the cable has frayed in the shifter. That’s relatively easy to replace, and worth doing, because if it has, then over time it will destroy the internals of the shifter.