UPVC seals/condensation

[Crensdale]

I moved into a house recently with UPVC windows that don't look very new. I've noticed that mould marks are appearing along some of the joins (see photo). I asked someone about it and they said it's just condensation, but if that was the case, why is it appearing only along the joins? It looks to me that the seal along the joins is going. If so, is it possible to repair it? I've seen there is some UPVC filler stuff available.
Thanks

 

[Wayners]

Condensation water settles in join and mould grows.

Just clean

 

[richw]

It could just be an area that catches running condensation, so goes mouldy over time. I'd start by bleaching it all off, then see what happens.

Good way to remove mould is to apply neat thick bleach to the area and cover with toilet roll which will help hold the bleach onto the affected area. Leave it for 12+ hours, then bin all the bleach-ey paper.

 

[RandomGrinch]

I may be wrong, but that looks to me as if it is the joint between the frame and the glazing bead.
The black gunk can be scraped out of the joint, and any surface muck can be cleaned off - No need for bleach, it's unlikely to be ingrained into the plastic.

If there is a build up of moisture here, it may be worth seeing if you can remove the bead and check the drains beneath the sealed unit are clear, so any water passing the window seals will dissipate to the outside, rather than just sitting in the channel.