I love my YM186D, the US version of YM1510D.
For my orchard that is
all uphill/downhill, avoiding making a full stop to shift then start uphill in a lower gear is a huge advantage. Also the ability to start in a lower gear then shift up while moving makes up most of the lesser hp compared to the YM240, because that one needs to start uphill in a lower gear than would be suitable after it gets moving. Overall the YM186D is more productive. That last top-end hp of the larger tractor is simply not needed in my application because the YM186D's gearing takes the place of it.
Price? $6,400 is pretty rich. These are real classics that deserve a premium price so if it checks out flawless that might be worth it. More typical would be to find one with some obvious flaws in cosmetics or some repairs needed, for under $4,000~$5,000. These are, after all, nearly 40 years old.
Photo, my first and then second YM186D's: 1) $2,500, no loader and obviously needed the steering box replaced. And 2) $4,500 asking price with loader and power steering. I got a better price on the second one only because the guy was in a total panic, he needed cash right now to get his truck fixed and get back to earning a living. It would have sold for $4,500 if he wrote a better CL ad than just 'Tractor, $1' and if he didn't sell it for the first offer.