Camshaft timed
Finally! After over a year (when we visited MiniSport, who told me the engine is down on BHP and compression, and the first thing to check was valve timing), the camshaft timing was checked. It looks like there was indeed a big problem in this area, namely a missing tensioner for the timing chain, which already caused a lot of wear on the chain. A new chain went in, along with the tensioner. The engine seems livelier, now, which is good news.