SP hub dynamos employ sealed bearings that do not require service until the bearings require replacement.
How do I know when they need replacement? Just ride it until seize and death?
Take the wheel out, hold it by the axle and spin.
If the bearings feel tight, check the pre-load.
If the bearings rumble, replace them.
@Heldring started
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SP hub dynamos employ sealed bearings that do not require service until the bearings require replacement.