Maybe worn out or broken mainspring?

I recently bought an old watch with the wostok 2809 caliber. I noticed that it could not be wound up that much until it's fully wound and also has a really harsh snap noise when getting close to fully wounded. The watch requires a shake to start so the balance wheel starts bouncing, in tougher situations I have to blow on the balance wheel or something to get it moving. The power reserve is somewhere around 5 hours it seems which is way less than it should be.

I have a strong feeling that the mainspring is very weak and worn right now but if anyone else has any toughs please share the. Also if you think the problem is the balance wheel do you know where I could get a new one (In Europe)?