Replacement part numbers for the engine coolant circulation pump on the M-25, M-25XP, M-25XPA, M-35, M-35A
The M-25 is built on the Kubota D850 block, the M-25XP and XPA are built on the Kubota D950 block. Both those Kubota blocks and the M-25/XP/XPA engines use the SAME coolant circulation pump. So the part numbers for either Kubota engine block will fit the other. However, you may find different part numbers for the same pump because Kubota's part numbers are keyed to the specific application, not to the engine used in that application (e.g. B6200 tractor, B7200 tractor, industrial equipment, etc.) So there are oftentimes different Kubota part numbers for exactly the same physical part (for example, the coolant pump.) Additionally, Kubota is constantly updating and assigning new part numbers, so the current part number for the coolant pump today could change to another number tomorrow.
Luckily, there is a good source for updated part numbers - www.messicks.com (an agricultural Kubota dealer that also sells online.) Messicks isn't usually the lest expensive on OEM Kubota parts, but it is a very knowledgeable source, the parts folks are super cooperative and helpful, and Messicks provided me with many of the Kubota parts manuals that are posted in the wiki.
Kumar Brothers (www.kumarbrosusa.com) sells many (but not all) Kubota aftermarket parts.
The current (7/2019) P/N for the coolant pumps are below. If you plug any Kubota P/N into the Messicks site, it will return the then-current part number, which you can use to purchase from any source you choose.
Westerbeke P/n 300203 (Universal) price: $385.30
gasket p/n 300204