If you have the plastic oil pan you may have a crack in the pan and a gasket won't be the cure ,those pans are a preventive maintaince item when you have about 500,000 miles on the series 60,I replaced 2 of the pieces of junk for the school here with metal pans, plastic pans are around 300 bucks and metal pans were 1200 bucks ea.
I'll be sure to take a look at the pan this weekend. If it's plastic, I won't even start the project until I have a new metal one (start saving $). Thanks.