depends on the type of equipment. If its a riding mower or something with a larger built in tank, then using the stabilizer is a good idea. The newer versions of Stabil are made for the modern gas with alcohol in it. If its a small trim mower where you can run it out of gas, then go ahead and do it. It won't hurt the seals at all. Any two stroke trim equipment such as weedeaters, blowers, edgers, etc, drain the gas out of them and start out with fresh premix in the spring. If you are putting them in the shed, some WD-40 wouldn't hurt on any of the metal parts that could rust. If its a piece of equipment that needs oil changed, I try to plan that for when I am getting ready to put them away for the winter. Then you are all set in the spring. Good time to sharpen blades, clean undersides of the deck, etc.