You could try this magic vegetable to free a stuck pully
This might sound unusual, and others have raised an eyebrow whenever I give this advice, but it works from personal experience. Take a clove of garlic, the fresher the better, and press it firmly against the stuck part until you see a drop of clear oil transfer to the part. Then, wait a few minutes remove the part. This method works on vehicles for me, even better than penetrating oil, so I don't see why it wouldn't work here.