And the big killer, washing down a hot mower in particular using the wash out port when hot will draw water into the bearings and cause them to fail in a single season.I have not heard anyone complain about the aluminum spindle housings on Scag machines. Scag aluminum housings are fairly strong compared to many other makes.
I have replaced both aluminum and cast iron spindle housings on many different makes. Moisture and dissimilar metals contribute to corrosion of the aluminum housings. Grass clipping accumulation under the deck will ad to corrosion/rust problems on any deck, keeping it clean and dry prolongs the life.