Need to see the recipe. Usually when a caramel, or chocolate sauce becomes seperated into oil, and other parts, it's because there was some kind of protein involved, such as milk, or milk products, and they've been overheated, causing the proteins to coagulate and break the sauce. Though I have had other sauces, without dairy, seperate as well.
Just recently, I made a ganache, and added another ingredient that did two things to the ganache. First, it cause the sauce to seize, that is, to partially solidify. Second, the sugar crystals became very apparent in what had been a nice and smooth ganache. The fat separated out, just like in your caramel sauce. I knew that no amount of stirring, or heating would fix it. But, I reasoned that sugar is dissolved by water. The additional ingredient added too much more sugar to the sauce, causing it to be a super-saturated solution. It absorbed too much water, and the sauce couldn't remain a sauce. So, I added more water, a couple tbs. at a time. This worked. I was able to save my ganache, though it was still more fudge-like in texture. Adding more water would have helped it even more. The water also dissolved the sugar crystals again. The result was very smooth, if a bit thick.
This might work for you as well. Try heating it, and working in water, a little at a time. If you think about it, caramel is an emulsion of sugar, fat, and water, with a bit of salt for flavor. The sugar binds together the water and fat. If the water is gone, there is nothing by sugar crystals and fat.
Seeeeeeya; Chief Longwind of the North
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