New Owner Op

Hi can any experienced guys out there with a C12 tell me how bad is a exhaust manifold gasket leak is... There is a guy selling me his 2000 FL with an overhaul engine with 220000 miles right now ... he wants to sell for 6000 he had it with fedex and due to fedex wanting the trucks to have adaptive cruise control he selling Because he can’t install it on the truck because it’s too old ... pls only experience guys reply