Dad taught me how to change oil about 30 years ago or so. The 1st tip he showed me was to put a bit of the new oil around the ring of the gasket on the new filter. The next thing was to not just look but run your finger over the surface where the filter screws into the motor and check for any remains of the old gasket.
Well yesterday I changed my oil on the Hemi, 7 quarts worth with a new filter and all went well until I went to leave work for lunch and found a big puddle under my truck.
Drove 24 miles to work and parked the truck, had to go to the shoppet to buy more oil and after removing the filter and finding the piece of the old gasket putting a new filter back on it cost me 5 more quarts of oil to refill the motor.

I failed to make sure the entire old gasket was off before I put the new one on I just looked while screwing the new one in place. This is the 1st time ever for me to have this happen but you can make dang sure I will use my fingers to feel the surface rather then just taking a quick look see from now on. Dads advice still hold true after all these years.
Fogy