Discovery 2a 2003 V8 4L (Australian)

Symptoms:
(1) Oscillating between only 0V and 1.13V readings in the bank 2 oxygen sensor (bank 1 normal)
(2) Had collected up error codes: P1171, P1174, P0150, P0174
(3) Exhaust sprays out liquid on ignition, quite a lot, then calms down mostly
(4) Exhaust fumes are sharp on the throat, very not pleasant
(5) Feels slightly underpowered, slower response, but not crazy slow
(6) Jolts sideways on ignition
(7) Bank 2 sensor sooty black
(8) Long term fuel trim 25% bank 2 (bank 1 at 2.34%)

Startup video:


Facts:
- O2 sensor is less than a year old (both replaced at once), Bosch
- Engine looked clean and new new when I had it open last July


Haven't checked:
A) Spark plugs, wires (less than a year old)
B) Bank 1 O2 sensor
C) MAF (less than a year old)
D) Fuel injector o-rings replaced in July
E) Fuel injector cleaning fluid
F) Haven't checked the idle air control valve, but I cleaned it less than a year ago, had a tiny bit of gunk then

What should I eliminate first?

Here we go again...

No idea, but following with interest!

Ok so you've got lean conditions on one bank and a green pin on the o2 sensor.
Clean that up, contact cleaner etc get it nice and shiny clean.
Clear the codes and see if p0150 comes back that's for the sensor and likely because there's the gunk making a bad connection.
Take it for a run to get the sensor nice and hot to clean it up

Is Bank 2 at +25%? Check for an exhaust leak on that side - it'll let air in, causing the ECU to see it as a lean condition, and crank up the fuelling. Remember it's using the level of O2 in the exhaust to determine if it's fuelling enough. Even a small leak will pull in air between exhaust pules.

If it's -25%, there may be a leaking injector on that bank, actually sending that side really rich, except 3 cylinders will actually be lean - how to the spark plugs look?