When I had the sump off the Landy I put it back on with a combination of both - a gasket and a thin smear of hemetite. Not had any problems with it since, although I was surprised how much the bolts pinched up once I'd run it for a bit.
I always used a gasket; one side bonded to the pan and something like 'Hermerite Red' between the gasket and block: still wept though. I just apply a thin bead of an ordinary silicone sealant now: all dry.
blue hylomar every time, tried gaskets and didn`t last long before the dripping started, changed to the blue stuff and its perfect, and does come off easy to if you remove the sump at a later date