Thank you for the replies. My work is done. I removed the trigger, and was able to see the issue--I did have to use liquid wrench to help removing the sear pin though.
The receiver had machine marks where the trigger engaged the receiver, so I used a Dremel to polish (not removing too much) the marks away. Mikey is correct, you can remove too much metal if you go nuts with course tools or work too fast, particularly with a Dremel tool. I polished the trigger humps, the sear where it engages the cam lug, and the cam lug where it engages the sear with Arkansas stones. The receiver is smooth as glass now, you can feel the difference b/w the polished area and a non-polished area. Just need to reblue these areas now for some protection.
Many thanks.