What was found
AIRCRAFT OVERNIGHTED IN TEMPS WELL BELOW ZERO, WITHOUT PROPER PREHEAT. AFTER TAKEOFF, BREATHER SYSTEM BLOCKED UP FROM FREEZING MOISTURE. AT APPROXIMATELY 1000 AGL, THE LEFT ENGINE OIL PRESSURE BEGAN TO RISE ABOVE THE GREEN ARC. AS CREW BEGAN TO SHUT DOWN ENGINE, THE OIL ACCESS PANEL OPENED, RESULTING IN SOME OIL LOSS AND A MISSING DIPSTICK. ENGINE SHUT DOWN NORMAL, RETURN UNEVENTFUL. MAINTENANCE CLEANED AIR/OIL SEPARATOR, AND ASSOCIATED LINES OF MOISTURE. SERVICED OIL, INSTALLED NEW OIL DIPSTICK, GROUND RUN OK, RELEASED FOR SERVICE.