hi, I have this old Omega, I believe is around 1940s. Please help me with the price and exact year.
On the back appears 18k.

 

hello and welcome.
I don't think Omega ever stamped 18k on the back of their watches.... a big red flag.

also, have a read of this:
https://omegaforums.net/threads/vintage-omega-posting-guide.383/

 

Hi Watson. Too bad Sherlock wasn't there when you bought that watch to deduce that this isn't all it's cracked up to be.

Seriously, Omega only put gold hallmarks on the inside of the caseback. That's a dead giveaway that your watch has an aftermarket case, probably from South America. Not much value to a collector, and not as much gold content so the scrap value isn't so good either.

The dial is also very poorly repainted, which when combined with the aftermarket case, kills any value the watch has. Even if it has a genuine Omega caliber inside, it's not worth much. Worst case, it could be a complete fake. We won't know until we see pictures of the inside.

Sorry to be the bearer of bad news.