Tank seat and valves
A leak under the tank
De'Longhi gives owners no repair jobs. The manual: "If the appliance is faulty, do not attempt to repair. Turn it off, unplug from the mains socket and contact Customer Services." The US manual adds that removing the exterior, repairing or modifying the machine voids the warranty (1 year in the US plus 1 with registration; 2 years in the UK and EU). Treat this as Customer Services work: the methods shown are owners', named where they appear.
First, the manual: some water in the space under the tank is normal; dry it with a sponge. Push the tank in so its valves open.
Coffee Grump (technician): a leak at the tank connection is a worn tank-base gasket, reached with the base off; machines above serial 63724 have the newer gasket. A leak inside from the silicone tube between tank and pump: fit the newer tube "with a blue stripe".
De'Longhi's drawing shows the tank seat (7313285109) with its gasket and valve ports under the tank; the US store photo of the same number looks like a drip tray, so check the part before ordering.