Blue smoke coming from exhaust at start up

Hey guys, I bought a 01 Sienna a month ago. It has 190k on it and has a good service history. Synthetic oil changes for the last 90k. The timing belt was changed at 100k. It has a new alternator, spark plugs and 02 sensor, brakes and tires. Last week I started it and blue smoke was coming from the exhaust for about 5 seconds and then stopped. This has never happened before. I was wondering if this has ever happened to any of you? I was told that the engine design is slightly tilted back from the factory causing an engine slug problem. My driveway is at a very steep angle and the Sienna was parked that way when the blue smoke came out of the exhaust. I have since started parking it in the garage on level ground and it has not happened since.