I came up with a DIY fix... don't know if it will work long term, but I don't really see why it won't.
I made a trip to lowes tonight and bough ta couple different size rubber grommets. The one that ended up working was a 11/32"ODx1/8"ID Hillman (SKU#008236716498). The grommet is slightly too small to fit in the hole in the WP-40 cover and the hole in it is too small for the impeller shaft. I needed something that I could insert into it that would stretch it to fit in the cover and also leave a hole large enough for the impeller shaft to sit in. I dug through my junk drawer and found come really cheap drywall hangers that were just the right size to slip over the impeller shaft.
I cut the end off the hanger, and trimmed off the hooks so that I could insert it into the grommet.
This assembly fit perfectly in the outer cover...
I reassembled everything and so far so good. The WP-40 runs "silent".... meaning it isn't any louder than my other one. Everything appears to be working fine... for now.
But if anyone does happen to have the correct replacement part or know where I can pick some up, let me know!