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.
Brake and Clutch Fluid
Check the brake fluid level in the reservoirs monthly.
Replace the brake fluid according to the time recommendation in the maintenance
minder schedule.
Always use Honda Heavy Duty Brake Fluid DOT ...
Engine Number and Transmission Number
See the image below for the locations of your vehicle’s engine number and
transmission number.
...
A/T System Description - Clutches and Gears (A/T)
Clutches and GearsThe five-speed automatic transmission uses
hydraulically-actuated clutches to engage or disengage the transmission
gears. When hydraulic pressure is introduced into the clut ...