Since it reads like you've done this a few times, How does the grease look and smell at your annual replacement?
I've never had a rear wheel bearing go bad on my Mazdas even with over 170k miles of street and years of track days so I would tend to think that they don't need regular replacement. Every season seems a bit excessive unless regular monitoring proves otherwise so I'm curious if you or others have noticed anything that would truly warrant a certain replacement interval.
Can you describe this Magaflux Dye thing?
I'm an IT person and it's been a good practice for me to have a known-good baseline to achieve success with anything which is why I start the year with this type of process. The rear bits are inclusive of an overall review of the major parts and whether they had been replaced during the year prior. In addition to the rear uprights/bearings/flanges, those other parts include front hubs (clean/inspect/regrease), lower ball joints and the upper boots (inspect for play or tears), replace all "lower suspension" hardware (adjustment bolts, rear outer long bolts), clean/lube sway bar bushings & end links, inner tie rod, ends & boots (inspect for straightness, play or tears), plus a full fluid swap (oil, trans, diff, brakes, blinker).
The odor from the grease has been consistent as has been the observed level of degradation (not measured or anything). The grease doesn't have the smooth consistency and overall coating property like it did when new. This would be expected for a 4-7 weekend race season of varied environmental characteristics (dry/wet, dusty, sandy...) I don't use the inner seal on the rear uprights so that is another reason why I do the replacement annually.
One caveat to the odor: when I removed the bearing from the bent upright, there was a distinct smell of burnt oil/metal due to the the heat generated in the bearing. It was not something I had smelled before at any point but it reminded me of how a hot engine with poorly maintained oil smells, like when you take off the valve cover for example.
Not to answer your question for the other commenter here, but magnaflux, I believe, is the "name brand" process of using a dye, magnetic particles, and an alternate light source (ultraviolet or otherwise) to identify cracks in steel/iron parts. My exposure to it was around the engine building process when you're building cast iron engines but it is usable across any industry where the integrity of iron/steel parts is a requirement (pipelines, ships...)
Here's the wiki entry for the generic term (magnetic particle inspection): https://en.wikipedia...icle_inspection
Edited by Brandon, 02-26-2020 12:30 PM.