Fix the leak correctly
Engine Stop Leak is a temporary fix for predominanatly seals. It has a "seal swell" in it, that in reality, doesn't know WHEN to stop and can lead to a bunch of messed up seals.
From their site:
INGREDIENTS
• Hydrotreated Oil
• Seal Swell
• Seal Conditioners
http://www.barsproducts.com/tech/E10L_tech.pdf
I'd be worried that it would do something else to the engine, despite the company's claim that it's safe to mix with dino or synthetic and won't block oil passages.