Bernie Hunt wrote:
....

You bring up an interesting point. I may be able to bust out the upper riser
between the two bad stairs. That might give access to the upper and lower
tread for clamping. I would then just have to replace that riser. I'll
experiement and see if I can tell if that riser sits ontop of the lower
tread. If it does then I may be able to get it out.
....

OK, I let it load the images. Even w/ magnification it really doesn't
look to me like either end of the tread is housed.

Since the stairs are enclosed on both ends, how could they be unless
those are skirtboards installed after the treads were already laid or,
if housed into the stringers they treads had to have been inserted from
the rear before the ceiling below was finished.

Have you unequivocally proven they really _are_ housed?

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