My Toyota 3MZ-FE engine valve cover gasket rear bank is leaking.
There's a Fel-Pro VS50588R copycat kit, which matches PN 11214-0A010,
11214-20030, 11213-0A010 & 11213-20030 (both banks & spark seals).
But the material isn't stated, so I can assume it's a nitrile-butadiene rubber & not a vinyl methyl silicone (or they would said that it was).
How important is silicone rubber for an aluminum V6 valve cover gasket?