How old is old? Longer then 3 years or something like ten years?
If there is no other reason for the leaking PRV, other than the spring finally got old, then a simple replacent should do it. The hardware stores carry them on the shelves down there.
Most of the plumbing parts there remind me of the US, except for how they run the pipes in the wall.
If after replacing the PRV, it still gives you trouble, then it could be something like the thermostats, thermal expansion or high water pressure.
I would change the PRV first.