P0135 O2 Sensor Heater Circuit - 1998 Toyota Avalon

My wife has a 1998 Toyota Avalon with the V-6, automatic (don't think they made a stick), 120K miles that got the engine light on. Checked the codes and it reads as a P0135 O2 Sensor Heater circuit.

A quick look at the car shows only O2 sensors in the exhaust manifolds, nothing near the catalytic converter. So is Bank 1 the closest to the firewall or up front? Also should I use any special lubricants on the threads before installing this? Should both be done at once as one is easy and one is going to be a real pain?

Dealership says $157 for the parts and $95 labor, ouch.

Bank 1 is the bank that has the number one cylinder.
In this case,its the cylinder head closest to the firewall.

Bank 1 sensor 1 is in that exhaust manifold.
Bank 2 sensor 1 is in the front exhaust manifold
Which one is showing as faulty?

You can use an anti-seize compound on the threads..new ones may have it on them already.
If not,make sure you get one thats oxygen sensor safe and apply to the threads only.
 

PO135 is bank one, sensor one. Front cylinder on pass side. This does use a downstream O2, by the way. It should be aft of the catalytic converter.