Tried to figure it out, compared it with others on the Internet..but are still not sure if this is a Flat 4 Bezel Inlay. Opinions or hard facts appreciated

 

My opinion only as I am not an expert...I am going to say 'yes'.
Although the pic is not detailed enough to get up close, I would say the serifs on the 4 point to it being so.

 

Yes it is.
I’m not an expert either, but my 5513 has a later service insert that seems to have both slightly thinner font (the tell is the 10 as far as I’m concerned) and a pointier 4

 

The OP inlay is period correct for glossy 5513's while @MaiLollo is thinner which indicates a service insert.

 

Thanks for the input all!

I mean I can see it has a flat top on the 4, but wasn't sure if other inserts don't have it either and are also not aware of the other details relevant.
So..looks like I have a flat 4. The 5513 is - according to the serial - a 1985, first generation glossy dial.

 

The OP inlay is a mid 80's insert (aka mk4), that you usually find from 1984.
Here a table that shows Sub's insert differences/period and a few shot of some of my 5513 wg with a mk4 insert.

 

Strange how differently thick luminous material on hands an indices can have exact the same colour seen from above, no matter what light, stunning if you consider accepted scientific knowledge...and they all look like from the same mother.