was enroute from Lloydminster to Estevan at 17,000 feet, with 5 people on board. When the a/c was about 35 miles southwest of Saskatoon, the pilot advised ATC that he was shutting down the right engine. He declared an emergency and requested to divert to Saskatoon. The a/c landed safely on Runway 27 at 0107Z with CFR on standby. OPI - System Safety UPDATE During cruise, the pilot noticed the oil pressure falling. He shut down the engine as a precaution and diverted to Saskatoon. Maintenance later reported that the problem arose when the idler gear studs backed off, allowing the gear to fall off the back of the engine. The resulting 1.5 inch hole allowed oil to escape and reduce pressure. The idler gear has been re-installed and the engine run-up without problems. At this time, the reason for the backing off of the studs is not known, and maintenance is communicating with other AMOs to determine the frequency and possible cause. The company will also file an SDR with Transport Canada.