GoWesty frowns upon oil and coolant additives of any kind, and using these products will void the warranty on any GoWesty engine or transmission. There is nothing that you need to add to your transaxle, engine crankscase, or cooling system other than the recommended lubricants or coolant.
When it comes to "stop leak" products, our firm stance is: Do not use any stop leak products at any time, ever! The common philosophy behind these products seems to be, "Why fix an oil leak with an actual trained technician with the proper tools and parts when you can just pop open a can and pour it in?" If this sounds too good to be true... well, you know how the saying goes. Products that make claims like "transaxle conditioner" or "stop your power steering leak now" or "head gasket in a can"—if these products advertised the truth, they'd simply say, "Spend your money on this stop leak, and then spend a whole lot more after you ruin your transaxle!"
The products sold for stopping leaks in an automatic transmission or power steering, for example, contain chemicals that simply cause o-rings and seals to swell temporarily. Then they finally shrink back to their normal, worn-out dimensions: Niagra! Most of these products were developed for used car dealers, which should give you pause enough.
Cooling system stop-leak products are particularly heinous. They work by clogging... Need we say more?
DON'T USE ANY OF THESE PRODUCTS!