I don't know much to tell you other than I feel your pain. My daughter (now 8) loved her carseat. She even slept in it rather then the bassinett when she was first born. I couldn't get her to sleep unless she was wrapped and inclined.
Now with my son . . . if he so much as saw the car seat he would start screaming. It got ever so slightly better when he was moved to the convertable seat when he outgrew the infant seat at 10 months(he was too tall), but he would still scream whenever I went to put him the the seat.
The only thing that helped any at all is having my daughter distract him while he is sitting in the seat. He has just recently gotten slightly better, but he is also now 13 months. Now he only screams when he is getting buckled. Once he is in he is ok now.