advice needed on Omega Seamaster 18k "crosshair" 1959

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Hello fellow members of this forum,

I am looking to purchase a dressier vintage Omega in solid gold. I am new to the vintage world and since it's so easy to overlook things I thought I'd ask for the community's help 😀

Came across this Seamaster and would love to get your opinions, especially about the movement. It seems like new to me? I've searched for a few other examples of the 520 movement and they are all showing their age...
Could this be a NOS replacement?

seller says this about the watch:

Magnificent Omega Seamaster Vintage in solid gold (18K/0.750) dated from 1959.
In exceptional condition, the watch has no sign of wear and has retained its shine through the years. Dial, case and glass close to new condition.
Dial: The cross-hair dial is rare and superb. Golden Omega logo, baton hands and golden indexes in perfect condition.
Case: The case is made of 18K solid gold. Unishell case allowing access to the movement only from the face of the watch, often guaranteeing an excellent state of the mechanism.
Reference: 14735 SC-1
Movement: Caliber 520 with manual winding in “as new” condition. Impressive for a watch of this age. See photos. 17 jewels movement.
Vintage: 1959
Operation: Excellent time keeping, no significant delays observed. Manual winding works perfectly.
Original Omega crown
Glass: Plexiglas
Brand new genuine crocodile leather strap with the Omega logo. Metal pin buckle with the Omega logo

So my questions are:
- is the movement original to the watch? or is it a replacement or ...?
- Who has more insights? Would this be a good purchase?
- what would be a good price for this? Seller is asking €1900,-
- any tips or anything I might be overlooking, any and all advice is greatly appreciated!

Thx so much in advance!

all the best,
Steven