Painting, varnishing, or replacing wooden windows and interior doors?

if the doors are from the 70s, are the windows also from that time? Although back then good mahogany tropical wood was used and painted with the good = poisonous stuff, I would replace the windows. You can of course also just replace the glass, ic would only go for triple glazing from now on.

. More important than the brand is the "level" and Röhrenspan is just the second from the bottom. But I also have it and have been satisfied so far.

Sorry I mean the quality level of the filling. So honeycomb insert is the cheapest. Then comes tubular chipboard, although there are actually two different ones, namely tubular chipboard dowels and tubular chipboard panels (ascending). Then there is solid chipboard and finally solid wood (nowadays unaffordable, but some also think that it might even be worse than solid chipboard in terms of sound insulation). I meant, I also have tubular chipboard (panel) from Lebo (Lebolit-CPL). Even installed with my father-in-law (let's say he installed it, I just watched a bit more). They were all okay, once I chipped something off a door frame with a door leaf, so CPL is not super resistant either, but that would probably have happened with lacquer as well. Sound-wise, we don't get much more through the door than through the wall now, but if you want to achieve something like that, you probably need soundproof doors (they then also have a lip that comes down and closes the gap at the bottom of the door).