Won't start. Just clicks when I turn the key.

I drove 2005 nissan maxima se to the store when I came out it wouldn't start tried jumping no start, Just make a click noise from what sounds from the dash of the passenger side at first but after we got the new battery it now sounds like the click sound is coming from center under the hood. But all lights power on heater window work radio all work head lights come on and do deem while trying to turn it over. got new battery no start checked ground wires good. From what I can tell the fuses and relays seem to be working the battery reads at 12V but drops just a bit when I turn over the key. Now it was struggling to start but when I turn off the key then back on it start fine but it got me to the store it didnt get me home. The motor turns so it not locked up. But I did notice there was oil that leaked all over the wires that are between the battery and the motor once the air intake was removed did wipe them down but nothing changed I've google it, youtube it, and ask who I could bout it locally but it all leads to dead ends. Please any advice is got to better then what I have now. I just bought it uses drove it about 2 weeks then it died. Thank anyone with advice in advance