sounds like the tube is damaged, you need to replace it
2001 Celica GT-S Turbo1997 Supra TT 6speed1997 Celica 3MZ/1MZ swap1990 Celica All-Trac
Assuming you're running a GT, the 5SFE has removable spark plug tubes -- they're screwed in, with the threads sealed by a high-temp thread locker equivalent to blue Loctite.
However, that sealant prevents oil from working up onto the bottom of the spark plug. Oil from the top is typically due to a failue of the tube gaskets at the top, but since you've changed those and you've found a slit in the side of the tube, I'd agree with Smaay.
I'd love to know how this happened, if you'd care to update us when you replace it.
If you don't have a chain wrench, the other way to unscrew the spark plug tubes is to use two of the valve cover nuts. Spin one on upside down, then the second rightside up, so that the shoulders of the nuts are pressed against each other. Use a large wrench (e.g. a monkey wrench) to grip the bottom nut and unscrew the tube -- the upper nut will act as a locknut and hold the bottom nut in place. Don't forget to reseal the threads when you install the replacement tube; high-temp blue Loctite is recommended by Toyota, but FIPG will also work. Don't use a common RTV, however.
2001 Celica GT-S Turbo1997 Supra TT 6speed1997 Celica 3MZ/1MZ swap1990 Celica All-Trac
I will have another look at that tube and post the results
Thx