How to remove years-old unknown glue from vinyl siding?

start in a hidden area....https://www.hunker.com/13414818/how-to-remove-adhesive-from-vinyl

Any time I need to remove an adhesive of any sort from just about anything, I always give simple Mineral Oil a try. I always have a bottle or two in my home. Has lots of uses, and really won't cause any damage. If it's a thick adhesive I apply a good amount directly onto it using a rag or paper towel that I poured it on to transfer. If it's being difficult you can allow it to penetrate, and in a sense revive the adhesive, it can be easily wiped away afterwards. (Random Addition - I take pride in my kitchen knives and my sharpening capabilities of any type of blade European / Asian when using a basic pull through style sharpener (carbide or ceramic) I apply a nice coat of Mineral oil and leave it visibly "wet" when sharpening, the result is an easier gliding motion through the sharpening device, afterwards wiping the blade clean, and applying a small amount of mineral oil on a fresh rag and almost buffing it on the blade, the oil penetrates leaving the blade with a very smooth, conditioned type feel (not greasy or oily) extends both the life of the blade and duration that blade can keep a perfect cutting edge.) I have over 15 years of experience in restaurants and know the value of not only having the right tools for a dish, but having them in peak working order.