White lithium grease.
Get an aerosol can of it with the little red straw.
Remove the pressure plate from the clutch.
Push on one side (green arrow) of the ring gear and it should expose a little peek into the bearing races.
Shoot a teeny bit of grease in there. Turn the assembly 1/3 around and repeat.
Repeat 1 more time for a total of 3 shots. Wipe up any excess that may have gotten where it should not be. The friction pucks and metal surfaces cannot have any oil or grease on them at all, ever. If you shoot too much grease in there it will just fling out during operation and make a slippery mess of the clutch. Only shoot a teeny bit in there...
Here's a pic to help:
The other way is to remove the clutch from the transmission shaft. There are 3 small holes drilled into the backside of the ring gear that allow you to squirt grease directly into the bearings.