This happens to me frequently.I have no gadgets but this works for me.
Warm soapy water a little bit of a soak of top cap with drip tip removed.
scrub inside out with toothbrush and rinse and dry.
Find a nice chubby 810 ( I use the 502 drip tip but anything with leverage that fits fairly snug )and throw it on and let it set into oring for a bit to grab. Then turn left and right and it should free up. now put your original back on and set where you like it.
