I just got a heavy duty rotary tool plus a flex-shaft.

Any suggestions on the best or easiest to find rotary tool (Dremel) flex-
shaft lubricant?

I noticed at first the spring rattled a little in the shaft, I guess (as
they say) the lubricant has to spread around the area before providing
enough slippage.

They say to use little lubricant or the device will overheat.

Thanks in advance.