I have successfully re-used Otto gaskets on iron head Squares starting with the 1936 Cammy. I applied a substance which appears to be no longer available called plastic hermetite to each side of the gasket before re-use. I wouldn't do it on an alloy head Square because of the low amount of torque you can apply to these engines, especially the Mk I.
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.