THE PILOT AND PASSENGERS WERE RETURNING TO ITHACA, NY., AFTER A BUSINESS TRIP TO INDIANA. THE PILOT HAD DEPARTED UNDER VFR CONDITIONS BUT RECEIVED AN IFR CLEARANCE EN ROUTE DUE TO DETERIORATING WEATHER CONDITIONS NEAR HIS DESTINATION. HE WAS AT 5,000 FEET AND BEING VECTORED TO THE FINAL APPROACH COURSE FOR THE VOR APPROACH TO RWY 14, WHEN HE REPORTED THAT HE 'JUST LOST THE GYROS.' RADIO AND RADAR CONTACT WERE LOST SHORTLY THEREAFTER. THE WRECKAGE WAS FOUND 4 DAYS LATER IN A WOODED AREA. EXAMINATION OF THE ENGINE DRIVEN VACUUM PUMP REVEALED IT WAS CAPABLE OF NORMAL OPERATION. THE EXAMINATION OF THE ARTIFICIAL HORIZON REVEALED THAT DUE TO 'DIRT PACKED IN THE FILTER' AND EVIDENCE THAT THE GYRO WAS 'POORLY MAINTAINED,' IT WAS THE OPINION OF THE QUALITY CONTROL INSPECTOR FOR MID CONTINENT INSTRUMENT COMPANY THAT THE 'THIS UNIT WAS NOT RELIABLE ENOUGH TO FLY WITH.' THE PILOT'S PERSONAL FLIGHT TIME LOGBOOK WAS NOT RECOVERED, THUS, INSTRUMENT PROFICIENCY COULD NOT BE DETERMINED.