Are you applying the proper torque to the oil pan bolts? It may sound silly, but they do have a proper torque spec (don't recall what it is).

I am going to replace my oil pan soon, and was wondering as well if a sealant was needed. I don't think there is any on there now, but then again, my oil pan gasket is seeping...

As far as the fuel injectors goes, you will also need to replacing the sealing washers that go between the injector and where it seats on the head. They are cheap.

Chris Blanchard
1984 300SD 139k