For a Seiko, I'll also recommend https://www.theseikologist.com/. As his name suggests, he specializes in Seikos and has a large stock of vintage Seiko parts which are hard to source. Though, it's still not cheap. I have a broken Seiko chronograph from the 70s and he quoted $500 to just do the watch equivalent of a tune up. He can't give a better estimate without opening it up, which is understandable.

If it isn't a hardship, I do recommend fixing your dad's watch. Sentimental pieces are always special.