I learned a lot about soil studies and how to underwrite deals that may have issues with oil spills (EPA concerns).

I can see from your post that you do lay pad (underlayment) underneath the floors.

They looked for bare dirt on the outside within 5 feet of the house and we had to mulch any exposed area( or have grass).Floors are a big area for tracking dirt in and a painted house of this age has lead in the soil so one of our floor samples did cause us to fail the first inspection (just over the limit) so get a good cleaner in before the inspection particularly if there has been work recently done.

The TX soil/clay will continue to work and shift.

They wear the same 5-8 shirts and they are slightly soiled dirty.

For vanities we typically use wall-hung models (easier cleaning in student rentals) or 'furniture'-style and run the floor underneath either.  

Not wanting to rip out a fairly new show I sawed off the bad 1 X 6 from underneath and then held them in place while "sistering" 2 spans of 2" X 12" on either side of the 4" X 12".

Just hold the blade at an angle and you won't hurt the chip board underneath.

I scrubbed it off and peeled some of the paint, underneath, there are some lighter gray residue.

It's unlikely an inside issue damaged the foundation the way you described it - look outside: downspouts, wells, soil.