The biggest danger from over-full engine oil is that the crank starts hitting the oil and "whips" it into a froth trapping air in the oil.  Aerated oil won't maintain the hydrostatic cushion that you need in plain bearings to keep the crank off the journals and rods off the crank.  If you pulled the dipstick and it looked foamy or cloudy, you might have a worry.  If it just looks like regular oil, then it wasn't full enough to foul the crank and no damage was done.  Since the G is designed to work at extreme up and down angles which would raise the oil level a LOT in one end of the sump, my guess is that you can't approach that with a few liters overfill while driving the car on level streets.

My guess on engoil 000 300 is that it's 0w30 oil.  Maybe right for M113(don't know), but definitely way too light for the M110.  It needs 10w40 in cold weather and 20w50 in hot.  Call the dealer and get them to tell you which viscosity grade they used.

And never, ever go back there for service.  If they think your truck is a G 500, or that it needs to be treated the same way, they're idiots and don't deserve your hard earned cash.

-Dave G.