Ladies watch stamped AU

Picked up a jar of jewellery from a charity shop today- There were a few goodies in it including some silver but I wonder if this watch is trash or treasure?
I know most of these watches are plated and worthless. The outside of this one is unmarked bar AU. Googling tells me AU is gold but the ones I can find are followed by a number to indicate the plating.
Frustratingly I can’t get the back off to see inside yet (any ideas?, doesn’t seem to be a nitch anywhere)
No loss if it’s just plate but the acid test holds up to between 10-14k.
The slanted mark to the left of the AU on the photo is a lighting artifice.
I’ve not seen gold marked AU before so I’m learning here!
Thanks for any thoughts

 

There seems to be a letter in front of the A ? V?

 

I think that line is the edge of the stamp as it’s definitely not there in reality. Can’t see any other stamps after the AU. I’ll try getting the front off! It probably is plated but I want to be sure before I move it on

 

So the glass comes off and the dial but it doesn’t look like the movement comes out the front. Shall I just file it to see if it’s plated as presumably of no value unless it’s gold so I won’t be committing any sin by damaging it?

 

At least it’s not a disaster if it gets damaged as that must happen when you are moving furniture etc. Some of your job must be great when you find a hidden gem, not so much the grim things. There’s an idea for a new thread - weird and wonderful things found in house clearances!