Depends what it is really, from my understanding some are built to be serviced and some are just throwaway movements where the service would cost more than a new movement would.
The other factor would be the age and whether a suitable replacement is available, at 20 years old it might not be which in some cases would be a shame, especially if it's a sentimental watch.
As to servicing, I wouldn't know where to go unfortunately.
With my Tuna I'll be sending it to Seiko if it needs it, with some of the cheaper ones probably try to source a new movement.
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