Depends..is it old oil or low? Clutch and Engine share Oil.
How about the Clutch Lever fluid?
It's a Hydraulic Clutch so Knut J mentioned that because you change/fill the Clutch Lever Fluid just like the brake fluid. Your Clutch Lever Fluid might be low or old and skanky, or both
Clutch doesn't slip like you say so maybe clutch is just not engaging-disengaging all the way cause of that,
Hopefully that's all it is
I have an 06 D - If had to replace Clutch I would want to go with a HD Slipper Clutch Drop-in.