i had the same problem a few weeks ago with my 2500 symetre reel ?? It was stiff to wind and same deal , was all pulled apart and totally regreased / oiled but it was still stiff .
a few runs from a 60cm flattie seemed to sort it out somehow ??
I actually thought the reel had shit itself when it freed up and wound like normal again
Perhaps run the dog on it again and see if they can free it up abit . Put a cardboard fin on its back for a real fishing experience
Im guessing some gear or spline wasn't meshing properly and re seated itself with the drag running under pressure for 4 odd 20 - 30 mtr runs from the flattie