This is great info! and I've concluded that my old girl did, indeed, have both sour and impacted crop per odor a few days ago, and discomfort displayed with odd jerky head/neck movements. This became clear on Saturday after she threw up some sunflower seeds -- and I'd had her indoors for 2 days, no sunflower seeds on the menu. I read that mineral oil can help, but you have to be very careful about administering, particularly with a syringe, as you could inadvertently cause death if they inhale it. I took away all food, and fed yogurt, loosened with a little mineral oil, kept water with electrolytes in the cage, and gently massaged her crop a few times. She threw up a few more seeds Saturday afternoon and a little more Sunday. Then today (Monday), and not to be gross, she clearly passed what's been stocked up based upon her output. She's looking and clearly feeling a lot better. Her crop is still a little enlarged, but no more craning her neck, acting distressed. On the road to recovery!
This is a great forum, and amazing what some sharing of information can do to save animals from distress, or worse. Thanks for your info