Just to close the loop on this one, I ended up replacing the entire pump/housing assembly. In order to do so, most all of the ABS components also needed to be replaced.
While I in there I ended up adding a second elbow to the outlet port of the Sanicon and directing this pipe (and the ultimately the flex hose) below the housing towards the large center hole in the bin. This keeps the hose from kinking so much when routed out this port in the bin and also keeps the hose away from strut on the bin door (which always seemed to rub).
Also, while the traditional slinky connection worked fine to dump the tanks after the pump gave up the ghost, opening that cap and then disconnecting the slinky after dumping was not pleasant. Due to the design of the pump housing, about 1" - 1.5" of waste water is retained in the bottom. This likes to run out when the cap is removed. So, rather than replacing this with the original hub-to-lug style fitting, I added another 3" waste valve here in case I have to use it again in the future (hard to see in the pic, but the black handle pulls horizontally towards the hose reel).
After getting the old assembly out, I tried to take it apart just to see if I could figure out what got lodged inside and likely caused the failure. Two comments/notes from that:
1) As mentioned, it does appear that the pump itself could be replaced. It's Thetford part number 97508, although I never came across any for sale online. Assuming you could find one, it's removable via the top, but the 4 screws that mount it inside the housing were incredibly corroded. I tried to get a couple of them to loosen up, but, as you could imagine, it was messy.
2) The manual illustrates a clear access panel on the bottom of the housing (I didn't even know this was here). According to the manual, this serves two purposes - a) to view the impeller to see if there are any obvious obstructions and b) to remove the impeller cover to remove any obstructions if found. While you can see this clear access panel from below the storage bin with the center cap removed, the consistency of the water remaining in the bottom of the housing does not allow you to view the impeller even after flushing the tanks for a while (your results may vary). Before taking it all apart, I removed this very carefully and let everything drain out into a bucket. I could see the impeller at that point and could actually spin it with little effort. I could also see the screws that mounted the impeller to the bottom of the pump. Although the manual specifically says to remove the impeller via this access panel, I could see any way that would be possible.
tl;dr - if this happens in the future, I'll just replace the entire pump/housing assembly again.
I'm adding the parts below just in case it helps someone else (and so I can find it when I have to do it again):
97518 - Qty 1 - Thetford SANI-CON Macerator Pump TOILET COMPONENTS RV
344632451 - Qty 2 - LaSalle Bristol Street Elbow Fitting for RV Sewer System - ABS Plastic - 90 Degree - 1-1/2"
344632891 - Qty 1 - LaSalle Bristol Adapter for RV Sewer System - ABS Plastic - 1-1/2" FPT
34466ND14AAR - Qty 1 - Bristol Double RV Waste Valves - Elbow - Rotating - 3" and 1.5" Hubs to 3" Spigot
34466N5A - Qty 1 - Bristol Waste Valve for RV Black Water Tank - 3" Hub to 3" Lug
632278 - Qty 1 - LaSalle Bristol 3X90 ABS 90 Degree Elbow
5817 - Qty 2 - NIBCO Cap Hub - ABS DWV, 3"