It would help if you named the brand and model, there isn’t a ‘one size fits all’ answer to the question.
Unlikely on a watch this age, but it could be a broken mainspring. If that’s the case it could be changed without fully stripping the movement but that’s a judgement call for whoever works on it. There's a good case for fully servicing the watch given the fact that it’ll be partially stripped anyway.
Owners are notorious for not giving the full story when describing problems, has the watch had any recent traumas?