Percival P. Cassidy wrote:
....
I'm assuming this is a steel-frame as well ...
No. Wood frame.

OK, some flexibility there, then, but last choice still...

....
I have removed the new seal again and closed the door. Now I can see a
wide gap at at the bottom at the hinge side and almost none at the lock
side. The gap at the top is the same all the way across. The adjustable
threshold is in its lowest setting all the way across. Conclusion: the
lumber supporting the aluminum threshold is bowed or swollen. I cannot
see how to remove the threshold.

More likely it was simply framed square on an out of level floor to
begin with altho it's possible something has happened since. One
disadvantage of the metal doors--can't easily trim to fit an
out-of-square door to account for such realities.

May have to remove the door entirely to remove a metal threshold if it
was put in and the door framed over it. But, some of the metal ones can
be removed if the leveling screws are taken out. What to do
specifically depends on the details which can't see from here...

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