I have a 6L stick with stop ring & 1x1 cone stuck together. I've been trying to separate them without success. Any advice?
Immerse the stuck assembly in soapy water, swoosh them around a bit, then try again. That should do the trick. It is okay to wiggle the piece a bit from side to side to try to loosen it up. Even ABS plastic LEGO pieces are somewhat flexible and they won't break if you flex them a bit.
If nothing else works you may have to resort to plyers. Use the kind that doesn't have ridges, so damage to the plastic remains minimal. Also, use shop gloves or something similar to make sure you have a good grip on the end that you are holding with your hand.
If you do resort to using pliers, try putting a wide rubber band between the pliers and the pieces to further reduce the damage to your bricks.
Use two pairs of pliers (one on each brick), that worked for me.