Well 26 years ago i dont think there was such a thing as house wrap, and some siding etc that ive replaced, had a type of roofing paper between the ply sheathing and vinyl. Its more common these days for OSB sheathing on outer walls covered by a house wrap, most good building supply companies carry it in stock, they will explain to you how to go through the stages of repair but its pretty basic, and you shouldnt have any problems if your going to tackle it yourself - but myself I would get in someone who does remodels, they would be far quicker, and most will save you money and a lot of time.