A family member recently passed an old oil lamp we’ve had in the family for quite a while, it had been left with old fuel in it, which had gone bad, and left some brown residue inside, which was entirely resistant to cleaning with soap and water, and also didn’t want to dissolve into fresh fuel.
After some work, I found that isopropyl alcohol is quite effective. I put a little bit in the reservoir and between letting it sit a bit, and swirling it to get everything, the lamp cleaned up nice and easy.
