My oh had a baby corn (3 months) who refused continually, the only way she would feed was if i split a pinky in half and fed it to her 1 half at a time. did this for 2 feeds, then left one in the rub with her overnight so she had a little privacy and she ate it fine. never had any probs since. as far as the mouthrot goes, i have no experience of that, so sorry i cant be more help.
Hope that is of some use to you, or someone with more experience advises.