Sea dweller repair

[Texasrecurve]

Hi I am new to the forum and have a question. I have a Sea Dweller I bought new in 1982 or so. It has been my everyday companion all this time. For the last few months it started losing 5 min a month or so and now it will not keep good time at all. It has never been serviced because I never had a problem with it until now.

1) Did I make a mistake by not having it serviced every few years?
2) Who do you recommend I send it to for service?

Thanks a lot for any answers!