Following up:

1. Plumber is concerned about getting parts for this specific toilet,
especially the spud because he says it's kind of a ******* looking one
that may have been jerry-rigged anyway, and says he will be most
surprised, given the shape of the mounting bolts on the floor (very
rusty and crudded over) and the fact that there are a couple of
cracks, non-leaking ones but cracks just the same, in the bowl, if
when he pulls the thing up to replace the wax seal it does not break
and become unusable anyway. That's why he advises total replacement.

2. She who must be obeyed ... i.e., the Mrs. ... says we're going to
replace the thing and she's already got some plans for the space
(mounting a shelf maybe where the brackets to hold the tank to the
wall are), so I guess we're going to replace the thing.

Thanks for the input, everyone.