I would not use it to replace Leen…..We use it when engines are having issues due to ethanol and it is just short of a miracle product. Just last night I had some seperated fuel in a small engine so I added the Startron and some fresh gas and cleaned things up a bit and got it running again smoothly and quickly. That said you could use it along with the Leen but I would stay with Mercurys recommendations whenever possible. I would also use of course Marine Stabil to keep what is in your tank together……We use Startron in Wheelers, Lawnmowers, Golf Carts, Go Carts, Wood chippers, Snowmobiles, Tractors, Automobiles, Outboards, Chainsaws, Trimmers and many other 2 and 4 stroke motors with great success…….and I do not sell nor work for that company……