Hey,
I feel for you mate, I just went through all the hassle of having a cracked head. Managed to get a brand new one for £520 all in (or around that amount anyway).
Get your head pressure tested before you do anything though as my head had two proper cracks found when pressure tested and another one that looked like a crack but the tester said it was not a proper crack and is very common this third one was more noticeable than the two actual cracks which could be what your seeing. Thats assuming your not experiencing all the symptoms of a cracked head in which case it could be a proper crack.
Sorry if that make no sense I'm being hurried along by the mrs. If I can help anymore let me know.
Cheers