A slab-on-grade foundation's West corner's supporting soils may sink in minor droughts = masonry cracks, etc as described.
1. you may dig out a deep flower bed at sinking corners, replace with compost/etc fill, compact & water deeply
2. get a structural engineer to test & advise
3. call Anchor Foundations for a wide budget guess then a visit
Lintels aka headers bowing in center used to be a common problem locally until the Building Inspectors began to adopt eng/arch specs in wood framing (or flitch beams).
Either learn what loads is carries above or assume ALL possible loads are bearing on it.
1. maybe there's room to jackup to level+ then sister a properly designed beam to it, calculated by the lumber co PSL supplier in HOU
2. maybe an engineer can design something steel plate to sister to it
3. the lumber co's top framer ref might be experienced enough to Guess what to sister to it
"Ten Word or Less" sigh - still working on it
Ten words or less ... a goal unattainable