Putting too much oil can damage alot of things in an engine if you rev it too much.. the crank will make too much contact with the oil and make it froth up and eventually you will get air in your oil galleys and can spin bearings, and ruin all kinds of things with putting too much oil.
A quart under is much better then 2 quarts over.
Will it cause a leak? I doubt it, though Ive sometimes left a dealership with more problems then when I came. Last time, I had just done a fresh brake job front and rear, and brand new control arms, and went to get a 4 wheel alignment, when they finished the alignment they told me I was missing the anti rattle clip from one of my brake calipers and that one of my control arms had a tear in its bushing's boot.. sure enough, the anti rattle clip was missing, and a boot was torn.. but, i had *just* done the brakes and control arms personally not a week before that.. stealership sabotaged my friggen car..
Also you can get the aussie version of haynes for your car here, bentley doesnt make one for a euro/aussie version of the m3. BMW