I wouldn't use red, maybe blue. You may need to take it off sometime and that'll make it a lot easier. I never heard of one coming loose, I think if you tighten it up and use the special lockwasher behind it it should be fine.
A piece of copper, an old penny for instance, can be wedged in the gears on the other side to hold it still for tightening without any damage to the teeth.
The gear noise you hear is common, they're noisy little engines. There's a couple things you can do to cut the noise. A bit of grease (about the size of a pencil's eraser) put on the small gear will work its way onto all the teeth. SBP sells these weird sound deadening things that stick on inside the cover. They're like stiff tar that never hardens and deaden sound. I've had them since day one and I think they work, it's pretty quiet.
Don't overdo the grease, it can work its way onto your clutch plate and pads causing it to slip.
Let us know if your output shaft and sprocket's ok after you tighten that sprocket nut.
I would worry it might have gotten chewed up while it was loose.
Good luck to you!