Ic , I am not well versed with the retailers warranty , if they do replace with a newer model of similar pricing , perhaps it make sense.
No worries , I am asking as this is the first time I heard of a 4 years warranty add on haha.
As for the filter , I think you might want to avoid that brand , Steinzeiser, in the future. If you do a search , typically , people use Hoya , B+W , Kenko etc . A clear filter will do fine if its just for protection , cos Digital cams have no use for UV filter la, though some do use UV filter to act as lens protector.
But anyway , key is enjoy shooting on your cam !