Broadly speaking, the OC is up for all costs, including repairs and repainting of the adjoining apartments unless a) the problem wasn’t caused by a common property failure or b) the owner of the apartment concerned had damaged common property causing it to fail.
If there’s any dispute over this, it should be handled separately from repairs to common walls etc. In other words, the OC should fix your walls then, if appropriate, claim costs back from the owner.