Check your new starter after a while. We replaced our original because of worn bushings and a need to be sailing rather than wait for re-build. Got the same starter without the fancy "Made in China" sticker (18209N 12V 1 KW Starter) Same relatively inexpensive starter and it did have great cranking power and faster speed, but ended up failing as the cast Aluminum nose piece pressed on the clutch housing, developed a crack and then broke off! Yikes! Well...at $150 (for us) I got another and filed the nose piece down a bit and used some clay to make sure I had clearance. Worked fine for two months and then another failure as my partner was on way for two week cruise. Lucky I had taken the original starter in for rebuild ($50 new bushings) and it was ready to go. The original (and expensive Yanmar) has the cast iron nose piece as opposed to the Aluminum housing. You can see in your side-by-side photo the Al housing is a bit bigger and longer than the original (I got my own conparative pictures but a sad story.) For our second one, it may have been prolonged hard starting which may contributed to the failure - especially in cold weather as we can sail here 12 mo (20F to 90F). Turns out a shot of starter fluid cured our hard start problem. I'd get your old starter rebuilt and have it ready as a spare - takes about an hour for a rebuild, and the cast iron is way more forgiving of the hard diesel starting knocks than the Aluminim - that is just materials properties.
