We are purchasing a top (6th) floor apartment in a 6 story 1929 masonry/wood frame apartment building. The wood framed stiffening wall between the bedroom and living room has settled approximately 1-1/2" over 12' (at the mid-point of the 24' long wall). The stiffening wall runs parallel to and is mid span between the masonry bearing walls. The floor to ceiling height is consistently 9'-0" throughout the apartment, there is no give or creaking in the floor and no evidence of historic water damage so I think the settling is a result of settlement of the slab/footing under the stiffening wall and is most likely evident on all the apartments in this line. I will check the condition of the basement slab, the condition in neighbors' apartments below us when possible but I would like to know how others may have dealt with similar conditions. If the settling has stabilized, I can either live with the condition or level the sub-floor and install a new wood floor in the bedroom and living room. I'm leaning towards leveling the sub-floor by rough shimming with exterior grade plywood, final leveling with Ardex and installing a floating engineered unfinished wood floor, screening and Rubio Monocoat oil finish. Any advice, cautions, etc. would be welcome. Thanks