Although some folks consider it just a stop gap measure I used a Chevrolet/GM approved stop leak product that I got at a Chevy dealer to stop a small leak in my W20 heater core. It has been working fine for two years now.
I used all six pellets in the package because of the amount of coolant.
Did you know you can download a Chassis Guide from Workhorse? I think they have one that goes back to 2001 - you might want to check.
Also do you know you can download schematics and plumbing diagrams for your coach from Winnebago?
They also have down loadable VIN specific parts lists as far back as 2004 and maybe earlier. Since my coach is a 2004 that is as far back as I have tried.
Clay WA5NMR - Ex Snowbird - 1 year, Ex Full timer for 11 years - 2004 Winnebago Sightseer 35N Workhorse chassis. Honda Accord toad.