The E18s I have are nearly completely swelled so you can just tell where the slot was and that's it. I was going to put them in a burn pile but have found I can remove the grain from the liner with a 3/4 inch dowel, and then open the slot with a saw just enough to get the igniter in. With some Magnelite on the grain, I have been able to get all of them to light but only have put them in saucers and lately an Applewhite monocopter. They light after a few to many chuffs (see video) and were well worth saving for me, but I can clearly see most folks would not go through that.

https://youtu.be/3AB8NHYHNJc