I've mentioned this before - I got on Ebay and bought a starter with the same physical dimensions but higher output than what belonged on my YM240.
When I bought the tractor it had a poorly-rebuilt starter that was past the warranty date written on it with auto-wrecker's yellow paint-pen. I thought buying new was better than rebuilding that very slow one. I think original spec is 1.2 or optional 1.4 KW, I found a 2 KW starter listed for a 4 cylinder 40hp Yanmar that had the same dimensions as OEM. One change, the wire down from keyswitch to solenoid had to be lengthened a few inches, no big deal. This starter cost $99.
This more powerful starter still cranks frantically 10 years later. I recommend doing this if the original starter isn't worth rebuilding.
And 1) this could be the remedy, or at least a patch, for a low compression hard to start engine to put off rebuilding it for a few years.
2) These starters use the same small-parts kit as the similar Japanese automotive starter of the same brand name. A DIY rebuild using the proper kit wouldn't cost much. Look on Ebay.