I wouldn't put a thin wall sleeve in a tri-cycle. A thin wall sleeve won't stay round in the bore behind it. If it doesn't leak, a "pin" hole won't hurt anything. If it does leak, I would inspect the entire water jacket. If it leaks, and your casting is not rusty inside the water jacket, then your problem most likely came from rust in the bore, from the bore-side of the casting. That said, if the casting is otherwise sound, a sleeve isn't a terrible idea. I know the world has stepped the bottom and pressed sleeves in for years, but I prefer a flanged sleeve, no bottom step, and fairly light press. Grind prep, clean, and JB Weld the hole before boring for the sleeve. Then light press on a flanged sleeve. For the street, at least .075 wall thickness at finish size. You don't want to bore into water, but a flanged sleeve, light press, and thick-wall of the sleeve itself is better. Also using ductile material is better. I'm not a fan of sleeving all 8 in an OE block unless you are sleeving it smaller. Fixing one cylinder, or even two, the right way is a good plan. Sleeving more than two with a flanged ductile iron sleeve starts costing more than a 352-390 block is worth. Just giving my opinion........