#1 plug fouling

Recently bought a 94 Surburban with 174k. I changed all of the plugs when I got it an noticed the #1plug really fouled. Recently I checked it again and it is fouled.THe truck is also burning oil although it doesnt smoke at all,maybe a little at start up. I am suspecting rings or valve seals. Would hope it is just valve seals. Is there a way to tell?