Inherited watch without Omega name or model name on dial

Hi,
I inherited this watch from from my father. I think that he bought it in South Africa. I would appreciate if anyone could indicate which model it is. I have searched the internet but am unable to find one exactly the same, even though I would have expected it to be a fairly popular model. I am also concerned about authenticity. The watch does not have the Omega name on the dial or a model name. The back is plain stainless steel with no identifying marks. It keeps good time although has habit of stopping at random intervals!

You should ask a local watchmaker to open the case. There will be a number stamped in the case back and a number on the movement.

Some models had no names. If it's like mine, it should be 33/34mm and gold filled. My experience is not wide, but I think you should open the back of the watch to see the caliber.