1. You can change the oil yourself. The only supplies you need are the 7 quarts of oil, appropriate filter (which should come with a crush washer and oil filter housing o-ring). The only tools, a 17mm wrench or socket and a 36mm socket for the filter cap. EDIT: Do a search to find out how to reset the oil service indicator through the cluster.
2. Your mech should be able to handle an oil leak after "a few times." That's not a good sign.
I would call the mech, ask what kind of oil he put in, then find a different mech that specializes in BMWs or european cars at a minimum. Change the oil yourself with a high-quality synthetic--appropriate selections can be found by searching this forum.
Last edited by lcoleman; 10-10-2012 at 10:03 PM.