8 3/4" Leak

The center chuck is only about 5 years old. I bought it as a complete center section from Mancini Racing. I probably have 300 miles on it. This past winter I pulled the rear end, center chuck, axles to repaint it. I replaced the fluid with a 90W with the sure grip additive. I have put 0 miles since because, my next project is painting the car. I just noticed it leaking and I would like to replace the seal prior to putting the drive shaft back in.