I bought a used Wolborg Ms fairly cheap and noticed that the blade is really unbalanced for some reason. I thought it might be that the shaft is somehow bend or messed up. After further inspection I noticed they the previous owner probably tried to open it up trio since there are some scratches around the top of the core. 

Anyone maybe knows this problem and knows how to solve it ?

Can you send an image of the part you're trying to repair ?

...you typically can't open up HMS Running Cores. Once they're damaged, that's it, you'll have to replace it (or the blade itself) entirely. This is especially true for Bearing Core.