Compression good - plug fouling

[Ryanz]

Purchased my 72 K5 about a year ago. It had sat for about 13 years after being restored. It's fouling the #8 plug with sludge and oil. However compression is a solid 140. I have replaced guide seals as they were hard as rocks but that hasn't solved the problem. I hear some guys suggesting it could be an intake gasket but I have solid vacuum and truck runs nice when not fouled. The previous owner did put holly intake and carb on it. The rest is matching numbers block. The shop I trust recently did a bore scope and said there is scaring on #8 - but wouldn't that mean my compression should be bad if it's sucking oil through there? On the highway doing 65mph it will just about burn a litre per hour. Not near as bad when just cruising around the city. Would sure appreciate some suggestions. I'm being told it's more than likely a rebuild project this winter :/