Same starter on all the GM series Yanmars. The part number from Yanmar
is 128170-77010. Only available from a Yanmar dearer in your local area. Cost is about $400 US.
About the aftermarket starters,.... I think there are several makers of new starters like this. It's a very common design in high production so volume brings the price
down. Usually around $80 US just like common auto starters.
I've had much better luck than you with my cheap
starter on a 3gm30f Yanmar. Three years now, used daily as a liveaboard
with no problems. (Knock on my wooden head)
There is no good reason this simple starter design should cost $400. I wouldn't be surprised if Yanmar buys them from Hitachi for about 80 bucks.
I think a modern factory using CAD/CAM processes would produce a starter as good as the original regardless of origin.
However you have had more than one example of the "knockoffs" and they have let you down. So it is understandable that you would source an OEM replacement, and the cost would be justified.
Hopefully you don't have some unknown issue elsewhere that would cause even an original replacement to fail early. And I can't think of what that might be either.
Best of luck.