Well, had the valve seals replaced and, miraculously, oil consumption has almost disappeared
A very happy guy, me.
There's a simple test, by the way, you can do to determine if its rings or valves that are leaking. Plug in a compression tester, and test every cilinder twice: first in the usual way, and a second time after adding a spoon full of engine oil in the cilinder. If the second compression test has the same (low!) result, the valves are the problem. If the second measurement turns out higher, the rings are leaky.