Hello and welcome!
It's an Omega 14381 as you know and a Google search should bring up other examples. The -7 is an iteration of the basic design as I understand it so, probably the first batch was -1, the second batch -2 and so on. Sadly, no image or many extra details on the
Omega site.
The little scratched numbers are old watchmaker's marks, as you suspect. Nobody does this anymore and we just supply a receipt with the model and serial as the guarantee.
It looks all original to me, with the exception of the crown (possibly) but the bracelet doesn't appear to be an Omega one and I'd get rid of it as it will probably damage the lugs. If it were mine, I'd service the movement, polish/replace the crystal, clean the case, replace the caseback seal and crown, replace the bracelet and wear it. Don't let anyone work on the dial/hands or polish the case (but, that's up to you).
If you were selling, then £1000-1500 would be the price range I'd estimate so, insure for at least that. These are desirable watches and one that is unmolested is always nice to see.
I hope this helps a little and you get to enjoy the watch.
Cheers, Chris
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