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looks nice indeed ! a check of the movement should be in order ... even though thank to the case, these are not prone to deterioration by water ingress ...
I disagree. These are ~50 year old watches. They may not have a caseback but the tube seals still perish and water, sweat and humidity still get in. The blue lacquer on the dials of these Dynamics is extremely prone to water damage. Subsequently you see a lot of these with water damages dials, or re-dials.
This one looks all original to me.
I would suggest that the owner finds a good independent watchmaker and gets it serviced. Since you don't know it's service history, it would be prudent to assume the mechanism's oil and seals are 50 years old and knackered.