Watch Verification for this Datejust

[makaxiv]

Hi guys, my grandfather passed away recently and he left behind this Datejust.

Images here, and apologies for using imgur, these forums are little finicky about picture resolutions:
https://imgur.com/a/QIis4dJ

I wanted to check if this watch was indeed authentic, and what it's approximate worth might be (not that we would sell it). Also, the watch doesn't run, and when I unscrew the crown to try and adjust the date and time, it feels very sticky, for lack of a better word. Definitely can't wind it either.

We estimate this watch to be at least 20 years old, and as far as my mom can remember, he hasn't worn it for a few years, preferring his Cartier instead.

Thanks again guys!