I shall be interested to hear how you get on with this. Square Fours tend to run somewhat hotter than water cooled car engines to the detriment of rubber around the cylinder head area. The Mini type O rings on the valve stems of my 1948 4G did not live long, but then oil down the valve guides was not a problem once I had fitted new valves and guides.
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.