Corridorone,
You've worked on so many versions of this -- you're obviously passionate about the story.? And passion is always a good thing.?? I can't say I've followed every version, but here's the way the story seems to break down based on your latest version:
Protagonist:? A female art forgery investigator.
Character flaw: ??
Inciting incident: The appearance of the diary and what the woman finds in it about the stolen treasure
The objective goal: Find the stolen treasure.
Antagonist: ??
Stakes: ??
So after 51 words, I only have information on 3 of the 6 need-to-know elements.
Sad to say, but what she discovers about about her father, while important to the story, is incidental to the logline.?? It's a 2nd or 3rd Act story twist in the form of a Big Reveal.? It's what happens after she sets out on her objective goal (find the treasure).? And while loglines implicitly promise action and discovery to follow as a consequence of the objective goal, they don't disclose any of that.
A primary reason is that there is simply not enough space.?? As every version of your logline in which you attempt include the information about her father and her missing family demonstrates.? At 51 words, this version far exceeds the ideal maximum length for a logline ,30 words.? And it exceeds what I take to be the tolerable maximum logline? length of 40 words --a number I arrived in analyzing over 600 loglines for stories that actually got made into movies.
If you focused on just providing information that answers the 6 elements listed above -- and nothing else -- what would the logline be?