As said already, you can not carry out a conclusive "look see" without stripping the engine down and checking all the idlers, pulleys and water pump, even then you will also need to have a look at the inside surface of the belt as that is where the cracking starts, also remember without removing the waterpump you will not know if the impellor is cracking or not. Which all leads back to the correct action is just to change all that lot. By the way, when I got this lot changed in my wife's Polo with a BBY engine, the exchange VAG waterpump did have a metal impellor, so maybe just, in the first place request a VAG exchange pump and open the box while in the parts dept, if its impellor is not metal just reject it - for that reason. The plastic impellor is usually black where as the metal impellor will be plated metal colour.