Is there no information about how it is built in the prospectus? Can you contact the municipality to get the house's blueprints to see if there is an air gap or not? Is it a wooden frame or is there something else in the wall?
If it has worked since the 40s, it should already have become a problem, I think... on the other hand, we shower and wash much more nowadays and maybe have a different view on ventilation and heating which creates and traps more moisture than when it was built...
Regarding the fact that old houses ventilated themselves, you often had an oil furnace or fireplace that created a warm chimney continuously drawing out air and thereby also pulling air into vents or through drafty doors and windows. Today, the furnace may have been replaced by a heat pump or electric furnace that does not provide a warm chimney, windows and doors have been sealed, and so on, creating a completely different indoor environment.
Our house from the 50s originally had an oil furnace that was replaced by an electric cassette, and we have now installed a heat pump. Essentially no working ventilation, so we installed exhaust ventilation, and it made a big difference to the indoor air. We considered FTX but noted that the cost for it was so significant that it was not economically justifiable when we have geothermal heating.
