That brown slime could also be from not having any coolant/conditioner in the system and only water and it will do the same thing. Brown gooey slime as the algae will grow in the system if it sits for a long while and not used. Like they said offer him $2500 and let him know what it will cost for a new head and engine maintenance as if the cooling system hasn't been maintained then you can assume that the whole mechanical aspect of the car is the same. 
Bud
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1987 300D Turbo, 175k mi., 1998 BMW 323i Convertible, 1997 F250 4x4 7.3L PSD
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