Some times Tri-Flow will loosen up a machine pretty quickly. One day my little 7 year old grand daughter was applying drops Tri-Flow it on a stuck Singer 99. I had her try to rock the hand wheel every time she put a drop of Tri-Flow on a joint that should move. Then one time the machine broke loose. She hugged the machine. Then Wilbur who was 3 wanted that 'brown' oil for the stuck machine he was working on. Since he is so liberal with oil I had given him regular sewing machine oil. The machine he was oiling was older and someone had used some other kind of oil than the 99 that took a lot more brushing solvent on it to get it unstuck. It is the places you can't see that you have to unstick. Places where two parts move together. If you force it something can go out of alignment and then you have more to do than unstick a machine. You have to figure a 7 year old kido can't force it too much but a kido with just oil can some times make a machine unstick. That machine in the picture above will probably need solvent. I wouldn't turn a kido loose with solvent because they wouldn't know how to keep it off the parts of the machine that should never see solvent. But doing it myself I use a solvent as if I was protecting a kido from the contact with skin or breathing the vapors or getting in on clothing, walls and floors, etc.