2006 Sonata Starting Problems

I recently had a good bit of corrosion build up on the negative terminal of my 06' Sonata. I removed the wire from the battery and cleaned it as well as I could, with a wire brush and battery terminal cleaner. The problem I am having is it still is very reluctant to start. If I start the car soon after shutting it off, there is little to no hesitation for it to start. The one place I don't know if I cleaned fully is the space between the plates that make up the terminal connector, but the bolt seems to be epoxied on, when I attempt to remove it just begins to deform the connector. I have put approximately 700 miles on my car since the problem has started, so I don't think it is the battery or alternator, and The car has started every time, just hesitant, so I don't believe it is the starter. Thank You for your help.