Belts!!!
I just tested both power heads with their new belts, and both are now far more civilized. The white and brown one wasn't bad before, and is even better now. The difference in the burgundy power head is night and day.
In taking the bottom plate off of the burgundy power head last weekend, I discovered that one of the posts that holds a screw was broken off, I tried to epoxy it, but when I was screwing the bottom plate back on yesterday, it didn't hold. Fortunately, the other power head held a solution. One of its two screws was a replacement and slightly longer than the original, so I swapped it over to the burgundy one and it went deep enough into the post to hold everything together. I just love when I find what I need is already at hand.
I just wish I had a second set of wands at hand. Swapping the set from the 1279 back and forth is such a pain. I put everything back together on the 1279 and there it will stay. The 1746 is effectively sidelined until I can procure a set of wands for it. I've requested a refund with eBay on the grounds that the seller has not followed through with shipping out a replacement. We'll see what happens...