i ordered some parts from an outfit on Alibaba called "Sunity" (
https://sunity.en.alibaba.com/) for my YSB8. it took quite a few back-and-forth messages to order the correct parts (tl;dr - just send them the part numbers from the get-go), and then i had to wait out one of those country-wide holidays, but once they finally shipped i got them fairly quickly.
i got an injection
pump, HP
fuel line, precombustion chamber, and some various gaskets. the injection
pump, chamber and
fuel line were great and i have about fifty hours on them; unfortunately the gaskets they sent were marginal and i ended up cutting my own from gasket sheet stock. i also ordered a set of shims for the
fuel pump but what was delivered was so thick they were completely unusable. the savings over yanmar prices were significant even with the gaskets i threw away.
the YSB, YSE, YSM motors are based on a farm utility
engine designed to run pumps, generators, tractors and the like. yanmar
sold them in great quantity for decades. the
rebuild parts like the piston & sleeve, rod & rod bearing, injector, injection pump are all available and likely will be for quite a while longer.
there is a fair amount of video available on youtube of rebuilding these and related TS and TF series motors.