If it turns out that it is the #3 piston is the issue, than it will require a complete disassemble. Re-hone the block and install new rings, is my guess.
You can pull the head drop the pan and pull #3. Done this before. Nothing special, just sometimes awkward to pull the pan. But saves a ton of time.
If the ring expander has a problem no need to rehone IMHO; pop in a new oil ring and keep the existing top and 2nd rings.
Even if #2 ring was flipped, I'd be tempted to just install a new one and go, if I did not have too many miles on the motor. And not hard to hone in place if it needed it.
