Rick,
I assume you are not talking flange gasket, because being an updraught carb, it would not leak petrol from there. My guess is that you are refering to the float chamber, etc. A paper gasket must be used, and also check that there is no bow in any of the sufaces, to ensure the gasket pinches across the whole surface. A liquid sealer should not be used, because if any of the goo get in to the carb, and it is pretty likely, then it will block jets. I usually get my carb gasket sets from Carburettor Exchange, in Leighton Buzzard, but there are other specailists. The material they use is better than normal gasket paper.
I think the Morris sump had a cork gasket, any sump which is pressed steel seals better with cork because of the usual uneveness of them. Get a sheet of cork and cut out with a sharp knife and wad punch, I use Wellseal to seal it.