Hi Perry
I have had my sump on and off my car several times and it is fairy easy. My sump had been hit by a rock and had a dent in it which damaged the seal. The original sump does not have a gasket they just have silicone seal. If you are going to fit a gasket which I highly recommend that you do don't use a cork gasket use a hard type gasket. You can can buy the gasket paper from your local auto shop and make it to suit your sump. You can't buy one from Nissan and they don't make any. Ues Permatex® Aviation Form-A-Gasket® No. 3 Sealant Liquid. I had to panel beat my sump to make sure it was 100% flat before going back on. This can be done by putting the sump on a flat surface and make sure there are no gaps around it.