RWR wrote:
Gently remove what you can with a fingernail, then moisten an old wash cloth or similar rag with lighter fluid and rub. I use that to remove old JCII stickers, labels off of glass jars, plastic bottles, etc. An old tee shirt also works well. May take several applications, depending on how gummy the label is. Use a clean part of the rag each time. Simplest way I know.
I clean lenses often with a "Johnson Flush". In your case you don't want to use the flush method, but rather a cotton rag with Johnson lighter fluid in a circular, slow movement. Don't put a soaking amount on, but a little at a time and confined to only the area with stickum on it.
I currently have three cans of Johnson lighter fluid on my bench, and I don't smoke, nor do I have a real cigarette lighter except for a little brass Bronica job as a novelty.
Lighter fluid is found at all stores with a cigarette section. Johnson is usually the brand.