Ok I got my old 3.55 open unit out and ready to put in the 3.80 posi unit. When I put the old unit in about 10k miles and 13 years ago I sealed the gasket to the housing. It looks to be in good shape, no cracks or peeling. My question is do I still need to replace the gasket or would it be ok to use the existing one. I did not have any leaks before. I'm also going to replace the cooper washers. Thanks for any help.