The spring also control the shaft spins, it pulled the shaft on the core, keeping the shaft from spinning and makes the handle easier to control.
Medium Spring and spare O-ring included on every GL Core. You can buy Light and Hard spring separately.
For more info about GL core you can this article.
If somehow the user prefer wobble to have wooble, you can remove the spring and the oring.
Oversize Core recommendations:
13.5mm for Medium-Hard silicone tension.
14mm for Medium-Light silicone tension.
14.5mm for Light silicone tension.
For Hard Tension Silicone better use White Core, unless you have strong hand.
Maintenance is not mandatory, but when you have time you can lubricate the oring and the core top surface that makes contact to the shaft. It will helps to reduce friction and gave smoother operation. Use Silicone based lube for this application.