Kosteus kylpyhuoneessa

What kind of floor material? I'm assuming concrete, covered by ceramic tiles?
If the bathroom is original from year 1984, there's not necessarily any kind of waterproofing (vedeneristys) under the tiles, or it does not fulfill the current standards. Typically there is just a lightweight damp proofing (kosteuseristys), which may leak water to the concrete below, especially from the bond between the well and the floor concrete.

If the moisture was detected by a moisture meter from above the tiles, it is very difficult to tell if the moisture is just in the thin layer of plaster below the tiles (which is perfectly normal even in case of good waterproofing), or if there is moisture also deeper in the structure (which requires fixing). It is very common that some moisture is found around the well, even if there is nothing wrong. For more reliable measurements the shower should not be used for several days - any harmless moisture near the surface would vaporize before the measurement.

In any case, if Yhtiö will fix it, make sure that they do it properly. In practice that requires renovation for the entire bathroom, including also the walls, so that a proper continous waterproofing can be done for the floor as well as the walls. When the old surfaces are demolished, the structures can be checked for moisture in more detail (and fixed if needed). Typically Yhtiö will pay the materials, which are of same level as the originals. If you want something better, you have to pay the difference yourself.

It is also good to check if this kind of renovation has been done in the other apartments already, or if similar kind of renovation is expected for other apartments. It is expensive, and in the end you will be paying that as part of your monthly condominium payment...

If your apartment will be fixed (properly), that will affect positively in the price of your apartment. But if renovation for other apartments is still to come, that should affect negatively in the price (not always does)...