Replaced heater core in 1980 gmc truck, been smelling antifreeze occasionally since Winter. Took the internal heat exchanger box off, and the engine bay heater fan box off. Found a mummified mouse, and a .300 wm cartridge left by the prior owner (must have dropped through the defrost vent). For better access I took the internal fender out and the battery tray , all the bolts came out (thanks West Coast), cleaned it, fiberglassed an area of battery corrosion, repainted it. Cleaned everything up, lots of old foam rubber, replaced it with old-style fiber weather stripping to dampen/seal the flaps, put it together. Old fan motor was still ok, but its easy to access if it needs replacing. About 3 hours of wrenching to figure things out, 5-6 hours of cleaning and painting.