Are you sure all of them are leaking? Rearmain on these are usually good for 150-200,00 miles, front seal about the same, you have to drop the pan to do the Timing cover so do them together, If you have oil in the front it is more likely the WP & or OPTI seals in the TC. If you have oil on the tranny inspection cover it is more likely the rear intake gasket is shot, common on the LT1. Reach behind the intake ans see how oily it is. Check the intake bolts while your in there.