What seals are there that are accessible from the outside, or with the pan off?
Transmissions in general:
Torque converter hub seal.
Dipstick tube seal. Check dipstick tube for cracks.
Modulator O-ring. Not applicable on 4L80E
Kickdown or TV cable seal. Not applicable on 4L80E
Bulkhead wire-harness connector seal(s)
Output shaft seal--probably with at least an inspection/cleaning of output shaft bushing and driveshaft U-joint yoke. This may lead to replacing the tailshaft housing seal, if the housing comes off to install a fresh bushing.
Manual shaft (shift shaft) seal
Speedo gear/VSS seal(s)
Pan gasket
If I had a trans sitting on the ground waiting to be installed, it'd take quite a bit of will-power to not install a Transgo shift kit while the pan was off.