Agree to do not push the limits when the engine integrity is at risk. Main concern is to know if the rensioner and guide are working properly. If all is working correctly, 49mm is a quite proportional measure by the mileage, and means that still is chain there; but why the guide has not moved in the last 20000 km?, that´s the question to solve. I think that when new, the chain elongates quite fast until adapting with the working parts, but after this change, remains quite a long time without significative variations. So, before openning the cam cover I will take out the tensioner and check if the guide has a free play by pushing upon it. If yes, that will indicate all is right and I can be enaugh relaxed to be proud of how I save my engine.
Will post what I find.