[Spurious]

Your problems are common ones zdenko.

The verdict is in Dezza, I checked my rear window seals & all clear. Blew all the gutters out with compressed air while I was at it. Just peel the rubber back with your finger as you move along.
The outer rear window rubber strip is loose in spots though, kinda bugs me but a non issue really.

Mine too has surface rust showing where boot lid rubs bumper.
I just treated the radiator crossmember to some rust converter recently. It cops all the road debris.
Battery tray was flaking rust at 10 years. ('00 model)

I'm lucky that I've painted my car, so I've had the chance to strip parts off & inspect most areas.
That's how I found that mud spats actually trap dirt against the sills, so they got ditched!
About 2 years ago I bought some RANEX rust converter, what with surface rust showing on the diff I thought I'd give it a dose.

Days prior I Karchered the entire floor pan & allowed it to dry. (car on ramps & me underneath in full wet weather gear!)
Then I used a degreaser gun/air compressor combo, & with the car on a hoist I went nuts & sprayed the stuff in every nook, seam, corner & hole. Did the entire floor pan & wheel arches. Use a charcoal filtered mask if you do this.
Still looks spotless today & rust free.

Also people, get under your car, or if you remove the seats & carpet for any reason, pay attention to the zinc coated, oval shaped hole caps in the floor pan.
In my case, the glue had broken on a few in the rear floor & it allowed the cap to move underneath the sound deadener & let water in.
I scraped out all the deadener, removed the caps, treated for rust (although none visible) & re-sealed the caps to the floor.

Some areas of the interior floor pan were not treated to paint, only the factory zinc coating, undercoat &/or sound deadener. So it's worth a look if you've ever spilled a drink in your car!