Hey Scott,  

I have a 2005 Toyota Avalon with 156k miles.  13k miles ago I had to replace the front #2 bank valve cover gasket and seals due to an obvious leak around the gasket, not because of  the valve cover oil tube seals leaking. 

At the time, I did not replace the rear #1 bank valve cover gaskets and seals because I had replaced all the plugs and ignition coils at 126k miles and knew what a chore it would be to get to the  rear # 1 bank  valve cover to replace the valve cover gasket, etc.  Hindsight being 20/20,  I realize now, to be safe, that I should have replaced the #1 bank valve cover gasket, seals and ignition oil tube seals while replacing the ignition coils, etc., at 126k miles  

As of today, #1 banks gasket is  still not leaking at all around the valve cover gasket and there are no obvious signs that there is an ignition coil oil tube seal leak.  The engine has no codes and runs great.

My question is what would you recommend about replacing the valve cover gasket, seals and ignition coil oil tube seals to avoid a failure of the tube seals which would oil the plugs and ignition coils on bank #1?  

And, do you have any idea on a Toyota Avalon at what mileage the ignition coil oil tube  seals might start leaking and wetting the plug and ignition coils?  Or, should I just suck it up and replace the gasket and seals on valve cover bank #1? 

Thanks you,

Jim B