What I am stuck on, is why is that not enough? In my case, the dealer claims the WoF noise was still present after they did that.
Replacing the engine is rather expensive (just the part was ~6K USD), and I have a hard time believing they would
readily absorb that cost unless they had a reason. Thoughts?
Had you considered that your motor had failed while perhaps the GRU had not? Both failures fall under the same 'motor rumble' TSB procedure from both Hyundai and Kia. Owners of course also refer to both as the wheel of fortune.
It may have been diagnosed incorrectly, or both had failed.
This mechanic went through the same process with a Niro. As to costs, I don't see that those should influence a technical opinion without a good understanding of their business process.
Yet if that was the answer, replacing the reduction gear should take care of this.
Are you assuming that the defect has been corrected? There has been zero indication of that within the last 6 months. Several owners with replaced GRUs have been keeping me apprised of their early oil changes and they're all seeing copious particles early on. A few owners are on their third GRU, two on their fourth.
As for the motor, there are indications that the newer revisions are far less likely to fail. Note that revisions have changed on the motor part number, not the bracket that holds it in place.
To reiterate, my research has been focused
solely on the GRU and finding the most likely root cause for the failure of that part. I've looked briefly at the motor issue and although it's always been the tail-end bearing causing the noise, the reason for that is not proven. I found a design error with its axial (spring) preload being too low but don't have enough information to accept that this is the root cause. But there's nothing that owners can do anyway to mitigate a failure so it doesn't really matter what caused it. The preload would be easy enough for Hyundai to rectify and perhaps that's what they've done for later revisions.
Note that the TSB describes 'spinning' the motor shaft with a drill motor to detect a noise. There are a few videos online
showing this process and an abnormal bearing noise is easily heard. Nowhere in the TSB does it say to inspect the condition of the spline.
What more evidence do you need?
Had you considered perhaps a few other owners with similar information? That hasn't happened despite well over 100 reports.
I spent
months going down the rabbit hole of alignment and bearing layouts and in the end it did not pan out to something that could cause a GRU failure. See
here and
here for the gory details.
I've focused on and have considered all potential internal engineering defects and the ever-increasing evidence overwhelmingly pointed to the conclusion I've reached. Perhaps your spline did fail but there's no clear and consistent path as to how that could cause the GRU intermediate shaft bearings to fail, the most common items inside the GRU found in poor condition.