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Here is what i see based on the sequence of events;
1. Imaged before with a DSI -> No Coma Detected
2. Replaced Screws -> Mirror will tend to go out of collimation
3. Imaged with DSLR Camera using a wider chip -> Coma at side
4. Restored Original Screws
5. Imaged with a DSI -> Coma still present
I used your image as a reference to indicate the problem;
1. Your mirror has a very small "sweet spot" which causes the sides to induce a coma. Sweet spot basically is the part of the mirror where the image is sharpest. To solve this, either you need to replace the mirror (or probably the scope), or get a coma corrector (not sure if this will solve everything because you are using a DSLR with a very big CCD chip and might not cover for the coma adjustment)
2. The sweet spot has moved to an area towards the upper left (marked in cirlce) which indicates that your mirror has moved. An indication that your scope is not collimated. Use a barlowed-collimator to bring the sweet spot back the center field.
3. When you restored the original collimation screws and imaged with the DSI, it imaged the part (marked in square) where coma is still present. To bring it back to its original state, collimate the scope such that the sweet spot is placed at the center of the field.
Hope this helps.
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