My advice would be to clean the mating faces the best you can.If using a scraper/blade be careful not too gouge into them if aluminium.A slight bit of sealant wont do any harm if needed and in some cases will hold the gasket in place.Do not put loads on,when compressed it can go everywhere.The amount of times I have seen what looks like cheese strings in the pick up pipe strainer worse still it will block an oil gallery