Various damages to 20-year-old wooden windows from WERU

Hello everyone,
this is about the windows in a detached house built in 2004/2005: tilt-and-turn wooden windows (Meranti) from the company Weru.

1. Several windows have noticeably corroded metal parts. What could be the causes here? Moisture? Cleaning attempts with harsh chemicals by previous users? Leaky sealing gaskets? What is the most likely cause, and why are the others less likely?

2. Several windows have mildew or mold; what could be the causes here? Poor cleaning by previous users, dust settling, dust retaining moisture, dust starting to mold? Again: What is the most likely cause, and why are the others less likely?

3. On absolutely all windows, the hinges have noticeably large play. If you stand in front of the open window sash and push up towards the hinge or pull away at the bottom from the hinge, the window sashes can wobble about 8-10 mm. This is also the case with windows that are normally never opened, e.g. a tiny window in the utility room, it wobbles just the same. However, opening and closing the windows works correctly without sticking or jamming. Does anyone have experience specifically with Weru windows and know if this is normal? Does something here need to be adjusted? Or are the window mechanisms worn out and need to be replaced—which after 20 years of service life should actually not yet be the case?

4. On individual windows, sealing gaskets are noticeably worn—on all other windows they still look completely okay. Specifically, two windows are affected here that are often opened and closed (kitchen-garden and living room-terrace; these are floor-to-ceiling windows used like doors). Can the sealing gasket degrade that much just from frequent opening and closing, or has something else happened here? What is the most likely cause?

5. Does anyone have any ideas about the oil and grease deposits? To me, it looks as if someone sprayed something extensively here. Can it be determined more precisely from the pictures what this is? The brown substance in the first picture is quite thick-layered; could this be a yellowish grease? The one in the second picture, which is also wiped into the corner, could that be graphite spray?

Thank you very much, and best regards,
Marco

I'll keep it short and to the point. According to various threads, you have a completely normal house. 20 years old and the plaster is crumbling.

… and here you will not get any other answers than in the green forum. There the question was whether the tenants are to blame.

I'll keep it short and to the point. According to various threads, you have a perfectly normal house. 20 years old and the plaster is crumbling

Thank you. That is really extremely helpful. This is exactly the kind of information one turns to the assembled wisdom and experience of a forum for. Thank you.

Was it the tenants or not? It has to be cleaned first.

First of all, it needs to be cleaned.

Of course, when the renovation starts, the windows and frames will be cleaned first – logical. But wouldn’t it be better to take the photos of the original condition if you first want to find out what happened here, wouldn’t you?

- "Mold stains can be caused by faulty seals." Okay, that’s one possibility. But the question was: Are there other possibilities? Or are faulty seals the only / predominantly likely cause?
- "Play in the windows indicates poor maintenance." Okay, theoretically conceivable – but this completely ignores my above statements that ALL windows have this, including those that are rarely or never opened. And that despite the wobbling, all windows close cleanly. Wouldn’t totally worn joints be noticeable by sticking when opening and closing? Are you sure that such play is not normal for Weru windows? The question is still totally open.
- "Oil and grease stains rather indicate poorly maintained windows. Metal rubs on metal and then spreads during normal window use together with old grease" – how should I understand this: does "poor maintenance" here mean "far too much grease"? But that’s more of a side question.
- No one has commented on the corroded metal parts yet. Seals? Chemicals? Windows left open and it rained on them several times? Who has ever seen such metal parts and what was the cause there?
- Also still open (I don’t know if I asked that in the other forum as well) whether a rubber seal alone can break down like in picture 1 just from opening and closing the window. Or whether it could also look like that if, for example, someone sprayed oil on it and didn’t wipe it off.
- But there are plenty of explanations on how to properly select tenants and whether wooden windows are the wrong choice anyway.

I think I am asking comprehensible questions here, and I still hope that someone will seriously engage with this more deeply. If it helps, I can gladly post more photos – just tell me what you need. Also feel free to tell me if my line of questioning is unclear in any way, and I will rephrase.