All materials, including steel expand when getting hot. Start with the cleaning, then lubricate again. If all fails you can always bypass the stove damper using a pipe damper. Try not to modify stove if not necessary.Baffle doesn’t look cracked from what I can see. Maybe it does just need a good cleaning like u said but it doesn’t explain why the damper is hard to operate when stove is running hot. That would lead me to believe the puck is warped.