We have:
https://carbide3d.com/hub/docs/maintenance/
For an SO4 w/ a Z-Plus Z-axis, the linear rails and blocks will need lubrication with Mobil Vactra No. 2:
or, the Pro Maintenance Kit adds belts:
Shapeoko Maintenance Kit - Carbide 3D (which also fit an SO4)
Beyond that, keeping the rails and belts clean, verifying that the pulley set screws are securely in place, and the belts are well-tensioned should be it.
An SO4 maintenance adds Delrin V wheels and pulleys and eccentric nuts and allows rebuilding a machine to like new.
For a bit more regular than that there is the Machine Operating Checklist in the manual after pg. 84:
For a printable single page version see: