Cut on radiator cap rubber

[hotcoder]

Today when I opened my car's radiator cap, I found out that the water level was low in radiator but it didn't suck water from reservoir. Also I found a cut on the round rubber inside radiator cap.
Is the radiator cap faulty and needs to be replaced?

[Xulfiqar]

its scrap - buy a new one. This seal being broken means the system wont maintain pressure or create vacuum to suck coolant from overflow tank and will also be vomiting coolant/water from the fill neck too when the engine gets hot.

btw - clean your system and fill with coolant, its currently running on rust and water, which is terrible and will cost you a great deal lot of money in the long run.