You only need the external gasket.
It is more than likely that valve cover gasket. However! I did have a headgasket leak on mine, and it was replaced under warranty around 50k miles (not an easy or cheap job). It's very hard to tell where the oil is coming from because like everyone said, it's a mess when the wind blows it around at speed.
Draining the coolant and removing the radiators is probably my least favorite thing to do on this bike. Mine is currently apart for the 15k valve service and it took me 2.5 hours to get it all apart, and I think 2 hours of that was the radiator removal, lol. I can try and detail the procedure, but if I were you I would just spray some cleaner on the lower radiator and use a semi-soft brush (a toothbrush would be good) to work it in, and rinse it.
Radiator removal: if you just remove the lower it will be much easier. The top one is a PITA.
-Remove both side fairings
-Remove fan shroud assembly bolts (the bottom one at the front is very hard to get to--might need to cut an allen key to be shorter)
-Take fan off of radiator (pull backwards)
-Drain lower radiator using plug on left side (you can drain all you want but be warned-there WILL be coolant spillage AFTER you drain it, because there is still coolant in the bottom below the plug)--I like to stick a paper towel in the hanging hoses to catch any coolant drips
-Disconnect hose clamps and pull hoses off radiator
I'm pretty sure there's enough room to pull the radiator down/out at this point without removing the front shroud (big black plastic piece). Removing the top radiator is a bigger ordeal, because all of that needs to come out.
Just removing the lower should be straight-forward.
2014 899 Panigale