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, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.