I'm not familiar with UA's policy, but I know that DL blocks the bulkhead until the day of departure on most aircraft for people with disabilities or medical problems. Your foot problem should qualify you for a bulkhead seat.
Well unfortunately, that's not what I got. On the outbound flt to IAD, I not only lost the aisle seat but E+ - I'm now in a window sit near the back of the plane in what the CSR said was a designated disabled seat ( or rather a seat for the disabled - I hope the seat itself isn't disabled or even going to be an even
longer flight...). Website shows the flight to be full ( except for my now available exit row seat).
Better luck on the return to SFO in the same exit row but have the middle aisle seat instead. Fingers firmly crossed that I can change the outbound seat assignment at the Gate