Well, update on the SG saga: sold it. Some people said it was normal, others said it could be damaged, on the meanwhile I spent more time looking at the crack rather than playing it. I suspected it could have some slight damage on the wood itself because #1 if the paint lost a chip it defenitely took a nice knock, and #2 the previous owner had retouched the crack on the upper side, yet the retouch paint started to crack on me meaning something could be moving underneath indeed.
Good news is that I got back the money I paid for it and a small extra and I also got to own such a great guitar, after spending almost 5 years with my starter Strat I could feel what a guitar more suited to the genre of music I play is like and get a better idea what feels better imo. On the other hand it really saddens me to let it go, I really liked that guitar. Well, back on seeking for a new keeper axe, but if I found another one of these in good condition I'd buy it. So, I'm considering either another Epi SG 400 or Pro, an Epi LP Standard (yep I've said the SGs are more confortable and a better bang for the money, but if i got an opportunity on one of those, I quite like them as well) or an LTD EC256 - pretty much solid body, set neck, hardtail and passive hums.