Toyota Repair: Previa - continued oil leak, valve cover gasket, oil valve

Question
I have a 92 Previa van(140k) that started leaking oil-valve cover
gasket replaced, still leaked. Went back, they decided it was the
camshaft cap seal-made a gasket with silicone and put on
another new v.c. gasket. Still leaking(even worse as I recall)-took
it to award winning toyota dealer-said some bolts were loose!
Got it home-you guessed it-still leaking at ?rear part of gasket.
Are there some half-moon seals or plug seals possibly involved
here? Just bad job with the silicone? Should I go to a toyota
dealer or trust the first place to eventually get it right? Thank
you very much in advance!  

Answer
Take it back to any toyota dealer you like and tell them to replace the "DISTRIBUTOR O-RING" I don't understand why it was not replaced when the valve cover gasket was replaced it's much easier to do it while the valve cover is off and we normally replace both at the same time to repair this leak.