Engine has 281,000 miles. Collant disappears at about one gallon per hour. No visible external leaks. Pressure test shows drop when engine is running. Oil on dip stick looks good. Underside of oil filler cap is milky and some vapor can be seen coming out of small brass fitting in middle of filler cap. No loss of engine power apparent. Exhaust is clear on startup and when running(except at heavy load). Water temp 180-185 when running. Suspect intake gasket leak to intake passage or head gasket leak near exhaust valve. Any suggestions or solutions? Compression test next?