i dont think the upper timing gaskets can be replaced without pulling the valve covers. i would not just tighten the bolts to get the leak to stop.

DIY is pretty straight forward. remove the cabin air filter housing, the fans up front. that should give you plenty of room. i did it a few years back. i would go ahead and replace the valve cover gaskets, upper timing gaskets, and o-rings for vanos solenoids, cam position sensors, etc. when i did mine, all of the above had residue. take your time and go slow, especially when removing the valve covers. the eccentric shaft sensors in the back are made out of plastic, you have to go up and over them. very easy to break the "ears" off of them. i believe they are $500 each!! if you break em..

keep an eye on your oil level, dont depend on the sensor to tell you if the oil is low. on other BMW's i had, dipstick would be bone dry and no "low oil light" from the sensor.

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2000 E53 4.4
2011 E70 35d