Only when they are due...you look about halfway there!
Haha, that is one gunked up grinder...I wonder how well it would spin if cleaned?
I save my iso that cleans my grinders and mason jars that I stash my herb in, it is now a very dark yellow/brown colour and about ready to evaporate off. It is a few of years worth of cleaning, I will load the goo into some thick oil carts I have for the Quaser pen eventually.
Honestly I dont think it slows it down that much
I got the Large BCG recently, so I was able to compare a brand new BCG to the gunked up standard. It really isnt that much more difficult to spin at all. A little bit sure, but not super noticeable. A bit of drag, but not much. If anything it just confirmed that it isn't ready to be cleaned yet