Thanks everybody! I took it to the dealer and he was able to yank them right out, so I guess nothing is wrong. I think I had the seatback angle too steep when trying to remove before. I was able to get them out (with difficulty) when the back locks were just unlatched and pulling straight back, rather than up. I'll try Achilles Heal's suggestion and see if that improves things, as I believe I always had the rear seat locks unlatched prior to trying to pull it out. I've had 2 back surgeries and I need to be really careful with operations like this. I probably wasn't appyling enough force before, combined with too steep of an angle for effective removal. Sounds like a good job to train my strong 14 year old son to do! Thanks again for the suggestions
Tom