Altima,Emitting smoke out tailpipe after spark plug and valve cover replacement, no overheating, after a week spark have black oil deposi

I have a 2003 Nissan Altima with under 200k, it's my commuter. I just changed the spark plugs and noticed oil in the vavles. There were three broken seals and I replaced the valve cover along with the gasket as they don't come with replacement seals and are made of plastic. After driving for a week I had noticed initial white smoke at the start and after a minute it goes away but occasionally while driving I'll get a slight sputter and smoke come out the tailpipe. So after seeing that I pulled out the spark plugs to inspect them and noticed two of the four were black with deposits