I have a 2008 fleetwood Excursion with a rear radiator and a 360 hp ISC engine. There is a small leak that appears to be coming from the center of the engine below the front fly wheel or damper I thin...
I would NOT use a sealer until the source is identified. If it turns out to be a replaceable part or leaking hose clamp, you don't need a sealer to potentially clog smaller water passages.
Were this a small leak in the radiator, then possibly a sealer should be considered.