I use the 15-40 in lots of things. In my two strokes I usually use ATF. if you take a whiff of the gear saver and look at it they look enough and smell enough alike that I feel like I am using the expensive stuff. I have used atf in big and small two strokes for about 40 years with good results. It may be another alternative for you if you can't always get what you want. SAE 50 is specified for most over the road trucks that have the popular eaton/fuller transmissions and it works just fine too. very cheap. the synthetic version pours reasonably in cooler weather too if you are interested in trying it. You can find it about anywhere you can find oil for a car, a truck, or a tractor. clutch friendly stuff for me so far.
But the 15-40 never made anything slip for me that wasnt already in some kind of mechanical trouble.