The sealing rings are synthetic resin with chamfered ends. Check the condition of the sealing rings, and replace them only if they are worn, distorted, or damaged.
For a better fit, squeeze sealing rings together slightly before installing them.

Apply ATF to the new sealing rings, then install them on the secondary shaft.

After installing the sealing rings, verify the following:
The rings are fully seated in the groove.
The rings are not twisted.
The chamfered ends of the rings are properly joined.
Disassembly
Compress the damper spring, then remove the nut (A) while holding the
damper shaft with a hex wrench (B). Do not compress the damper spring more
than necessary to remove the nut.
...
Transmission End Cover Removal (A/T)
Special Tools Required
Mainshaft Holder 07GAB-PF50101
Remove the bolts securing the ATF inlet line (D) and ATF filter holder
(E), the line bolt and sealing washers, and remove the ATF in ...
ATF Cooler Hose Replacement (A/T)
Drain the automatic transmission fluid (ATF).
Install the ATF cooler hoses over the ATF cooler lines, and secure the
hoses with the clips in the details (A), (B), (C), and (D) ...