Is this common in the Fabia??

I'm guessing it is caused by the door water leaks

I'm having issues sliding my front passenger seat backwards and forwards, keeps getting stuck due to all the rust

The sliders are almost red in colour lol

Also an annoying creaking sound from the front drivers seat when taking a sharp corner, it sounds like it's about to fall off at times

I did read somewhere that the seat can slightly move down over a few days of regular driving, so it needs adjusting regularly but i don't think that's the issue here.

Fix the leak, remove the seats, dry the flor plan properly and treat the rust then re-fit.