Should we just re-seal the whole façade?
Usually not as a first step. Blanket re-sealing is expensive and may not address the actual path if water enters through gaskets, flashings, frame corners or the wall behind. Diagnose first, then repair the proven defect. If testing shows sealant has failed widely, a planned full replacement with proper joint preparation may then be justified.
From the RRD Field Guide, checked against the sources cited in Façade and Curtain Wall Water Leakage: How to Diagnose and Fix the Root Cause. General information, not advice for your project.
The fuller picture
Façade leaks are diagnosed by mapping when and where water appears, ruling out non-façade sources, then reproducing the leak with controlled water tests: AAMA 501.2 nozzle testing for curtain walls and ASTM E1105 pressure-chamber testing for windows and walls. Test from the bottom up, isolate one joint at a time, and repair the proven path rather than re-sealing everything.