Whatt causes oil leak to leak into the space above the top of the spark plug? on 2001 Toyota Camry

I had a new valve cover gasket installed, it still gets oil on the top of the plug (where the boot meets the plug).

3 answers 2 comments
I've heard there is a class action suit filed in 2014 because so many Toyota engines leak oil from a bolt that is stripped and cannot be fixed. I'll try to find the suit on the Internet and post it here.
Valve cover SET not installed properly or completely, spark plug tubes need to be resealed at cyl. head.
Thank you, but what is a valve cover SET?
A set includes all componets to seal the valve cover inclu. upper plug tube seals,ect.
To seal the lower part of the plug tube it has to be removed and sealed, best left to a mechanic,
or a savvy car person with proper tools! If the upper seals were not installed,or properly installed
oil will pond in plug tubes! This is the most likely scenario. However a lower seal will have the same results!
Usually the top seals fix this problem IF installed correctly.
Need plug tubes and valve cover gaskets replaced. Agree with wetry.