I think that Ariel did use a sealant - probably a shellac based compound. I tend to use a smear of Hylomar. I don't get leaks from the crankcase half joints because there always seems to be plenty of other places for the oil to escape.
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.