I don’t know what makes a synthetic biodegradable, but Amsoil doesn’t make that claim for any of their products. Having used their 2 cycle product when one bottle was good for any application. I question how much difference there is in all the different applications the offer today? I have used their gear oil in my manual transmissions starting in the 70 . They have a good product. I’ve decided to go with the Stihl ultra because it’s biodegradable and easy for me to get. Not making a recommendation. Just offering my experience for one to consider in this controversial subject of our hobby.
Use your best judgment.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.