You might be able to get by with some RTV sealant between the front cap and the front engine plate, but there does need to be something in there. Oil could seep out from the front of the front main bearing or out of the timing cover. The "right" way would be to remove the timing cover and front engine plate, and replace the gaskets and the front crank seal. Depends on whether your front crank seal is needing replacement too.
