I don't even want to tell you how long it's been since I changed it in mine. Since it's only used for a few hours each year, I kind of forget about it. To be honest, I only thought of it this time because it was apparently getting hot and shutting down after running only a few minutes. The oil was sludge. It's almost 20 years old, and I replaced the pump in it last year for about $40, because the motor was still running fine. Honda motors are incredible, and take tons of abuse. The Honda in my reel mower is also about 20 yrs. old, but gets serviced regularly, and still starts on first pull.
After looking around, I'm going to order this pump. Looks pretty good for pretty cheap.
https://www.homedepot.com/p/Lumax-Multi-Purpose-Hand-Transfer-Pump-LX-1345/302544982
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Same price at HD as amazon, and I don't have to give Bezos any of my $.