As noted by No Mercy, it's not a Seamaster and it never was since this is not a waterproof case, a requirement for a Seamaster.
Time keeping is not a particularly good indicator as to whether a movement needs a service, even a dry dirty movement is capable of keeping good time. A proper service would be $150-200 US plus parts if necessary.
Have you looked here:
https://omegaforums.net/forums/private-watch-sales/Click to expand...