I have the drawings for the Kestrel gearbox and there are no separate bearings DU or otherwise as such in the gearbox, just Glasflugel's standard ptfe tape and resin mix embedded in the shells of the gearbox. I think the stiffness comes from both the contraction of the resin over the years and the corrosion of the unprotected steel shaft. My Kestrel air brakes can get stiff, and I use a light ptfe lubricant half way along the shaft to creep into the pure bearings, as per JJ's method, and by taking off the small cap on the external end of the drive dogs (is this on Libelles? I think not...) I can inject some heavier weight oil onto the gears themselves. Needs to be done ever two or three years sadly but it makes the brakes usable. I keep thinking of a major rework and replacing the gearbox with a modern right angle drive.