This is the 6398th most frequent Polish word.
błotniku
"Błotniku" means "mudguard" or "fender" in English, typically referring to a part of a vehicle or bicycle.
This sentence uses the word "błotniku" as addressing directly an object, personifying it with grammatical vocative case.
Błotniku, musisz zostać naprawiony.
Mudguard, you need to be repaired.
Here, "błotniku" is in the locative case, describing the location of the scratch.
Widziałem rysę na błotniku.
I saw a scratch on the mudguard.
In this instance, "błotniku" is in the instrumental case, indicating the means or companion state of the action.