Whilst casually assembling e3d v6 kit, there was this one part left over, not mentioned in any of the videos or guides I observed. a tiny blue clip like deal. A bit of scrounging turned up of all things a thiingiverse file for just that item. Ah, now I see. Making sure the tube was properly seated in the heat break, the break thoroughly seated in the heat sink, I popped the black guide/lock into "the fully upright position" and confidently went to install the little blue clip. Which promptly popped off at a high rate of speed, apparently achieving dimensional escape velocity. Question now is to order a couple on Amazebay, or rely on the "lock" to keep the tube in position while I print what I found on thingiverse and change the tube working out while doing retracts?