I recently installed a Cummins RS25 25kW generator for our house and wanted to provide folks with some info.

For those that want a good deal on maintenance items for this thing - the genuine Onan part #'s for spark plugs are A044H806, and oil filters are A044D820. However, these are very expensive parts! I received some that I ordered today, and the spark plug is just an NGK BKR6E-11 plug, and the oil filter is a Fleet Guard LF3537. You can cross reference the oil filter online and find better deals than just buying Cummins parts that are re-branded.