that happened to me a while back. I just kept trying and with a few curse words, she finally popped out.
I guess you could gently pry it if you are sure you aren't bending/breaking something. I'd put a wood block or something under the fulcrum you use to protect the intake, perhaps a long screwdriver under the first lip of the distributor should work--maybe tapping the handle of the screwdriver down (not in) while pressure is being held may work.