I think you're talking about some "composite clapboards" that are typically referred to as "Masonite". It's really not much more than pressed cardboard, or fibreboard; and it is expected that it will be protected from water by a coat of paint . . . . and not submerged below a snowbank that, when it melts, will inundate the clapboards, and turn it to mush.
Is there paint on the Clapboards? The damage you're describing sounds like it's due to the lack of paint along the drip edge of the Masonite, and water has been allowed to soak into it.
The paint is what keeps water from being absorbed by the Masonite. If it is allowed to dry out, it can probably be re-painted. If it has deteriorated too much, then no paint will bring it back to looking like new.
I don't think water will penetrate it until it is really falling apart, or if water is allowed to travel behind or under it.
Whatever you do, get a coat of paint on it! Don't just allow it to deteriorate further over the next 10 years.
Dale C. Hittle of GOLDEN RULE PROPERTIES in Glover, Vermont
Where We're Always Striving To Put Together "THE FAIR DEAL"