I'm all OEM when it comes to my 525efis. For the impeller, waited three years, freshwater only, maybe but 45 hours on in 3 seasons, and had a cracked spline at the base on one of them. That's when I changed the routine to every other year, regardless of wear time, etc. Not the most fun job, but alternative is worse to have one come apart, etc....

I pull it when winterize and inspect them. To be honest, I boat in really clean water and I could easily go 5 years with the Merc impellers in the Hardin stainless housing. In the plastic housing I had to replace both every year. I change mine every 2 years just because I have it out. I now have a big box of spares.

I was changing mine every year. Then I went to 2yrs. After 2 years I took it apart and discovered water had got into the bearing. Went back to every year. Not worth the few dollars in savings imo.

I ended up going back with Mercury.

After my fresh water cooling install it is a pain to get my water pumps out. Have to remove the pulley them fsnagle the pumps out the back in between the offshore mounts. It's a real pain in the ass.

Mine looked brand new yesterday when I pulled them - and I just remembered that they are actually 2 seasons (both short and low hour) old......

I think I'm going to extend my routine to 2 years every time.