I have an Orient brand diver's watch, a "King Diver", from the '70s. It's a large watch, probably similar to your Seiko. I bought it new in 1971 for $40. That was a lot of money at the time.
I had it cleaned regularly for many years (about every 3 years or so) at significant cost just to keep it running but it really didn't keep time all that well. After 15 years or so of ongoing expense I stopped wearing it and now just keep it in a drawer. It's nice to look at but it's not very practical.
In the first few years of ownership, pretty much every jeweller/watchmaker could clean and service an automatic watch but that all changed as Quartz watches became the norm. In later years I had a master watchmaker (an authorized repair agent for Rolex watches) service it.
I now have a Victorinox quartz watch of a similar size that looks somewhat similar, keeps much better time, and only needs a new battery every 4 years or so.
My last Victorinox watch lasted about 30 years. It eventually stopped and has since been messed about by a local watchmaker and is no longer waterproof, so I use it on days when I might damage my watch. I could get my Master Watchmaker to have a go at it but I don't think I'll bother.
Having said that, one of my professors bought a Rolex in the middle east in the 1950s that ran without any maintenance at all until the early 1990s. It finally stopped and as he said, "Cost more to service than he had paid for it in the first place." The watchmaker was pretty clear that if he had had it cleaned and serviced somewhere along the line it wouldn't have needed repairs.