HensTeeth

Oil based. The advantage it has is that it never sets and will continue to creep into rust for ages after its applied. The downside is that it's messier than waxes which set to a greater or lesser extent and will wash off faster so it'll need doing annually, at least for the first few years, but it's quite good for rusty areas that are hard to get to. Sadly there's no one perfect solution once rust is present - it's all trade-offs. Speaking from personal experience of using their corrosion removal, neutralisation, arresting etc. products over more than 10 years is that the Bill Hamber range is excellent and does what it says it'll do, so long as you follow the instructions. Whatever you use, there's nothing that's a one and done. Everything is messier than a painted surface, but what good is not messy when stones and salt degrade the paint and it comes off. If you're doing it yourself and want the rust back to shiny metal, the poly strip wheels on angle grinders and drills are fabulous at getting rid of rust but not removing excess metal. The problem is you can't get them into most of the places you really need to get them into like all the pipework and intricacies of the subframes and behind. That's why BH suggest you wire brush and remove what scale you can and then just apply Dynax wax and keep a regular eye on it. https://bilthamber.com/faq/can-i-use-rust-removers-and-paint-coatings-to-protect-a-rusted-vehicle-underside/

Don't laugh, but check your front number plate. I've posted about this before, I think, but if there's a build-up of dirt behind the plate and/or its supporting plinth, the sensors seem to pick up the damp muck and interpret it as 'something very close'. Hence why it can come and go in damp weather. I did a thorough clean-up and reattached the number plate with new sticky things, and have had no more trouble. ETA - easy to see if it's going to help you - take the number plate and plinth off and see if the sensors suddenly start behaving...

Wheel bearing perhaps? What happens to the sound if you knock the transmission into neutral?

I would imagine that the computer is looking for a valid temperature reading from the sensor. It won't know where the sensor actually is, merely that it's electrically present and that the reading the computer is obtaining from it is within the expected range. So if the sensor isn't connected, the computer logs the fault because it doesn't know how warm the battery is, and so it doesn't know if it's overcharging it or not.

Probably wouldn't be your first choice, but is a conversion to a non-rear steer arrangement feasible, with a rack removal and replacement with tie rods? Mechanically likely to be easier than persuading the computer to let go of its amputated rack, I suspect

The YouTube video (about 2'27" in) in this thread shows the battery voltages in Techstream when you go to register a sensor. Maybe that's where it is? Though I'm not sure 'OVER' as a battery voltage is much help...

Anywhere with birds, they do that... Worse, much worse, I've noticed, when the car is was spotlessly clean. If you're planning to update the maps yourself, the guidance they provide is decent, but make sure you use a decent USB stick. Doesn't have to be fast - I've tried a faster one, and it made no difference to how long it takes, which is best part of 80 minutes. I've done it twice now, and the first time I did it just sat in the drive with the car in Ready mode; the second I went for a drive.

Gulp. You're thinking that stripping the rack down to its constituent components should identify the root cause, with a replacement from Amayama as a backup plan? I'm very interested in how you get on...

That YouTube video, complete with clicking relays, looks like classic symptoms of a low battery voltage. If you have a multimeter, check the voltage at the battery both with the car off and when you're trying to start it. Anything much below 12V and you'll have issues. If you've managed to get it fully charged from an external source (mains charger like a CTEK etc) and you're still having difficulty, and the battery voltage won't stay above 12V for more than a couple of days, you've either got a parasitic drain on the battery, or the battery is kaput. If it's the battery, Tayna now do one which looks an exact replacement for the MK4 GS450h

I've used this crowd a couple of times for map updates which seemed a respectable deal - others are available. Seems new maps for the earliest of the Gen 4 GS have stopped now, but you can get updated to 2022/3, which is good. I've idly wondered about installing a BeatSonic, Grom, or Carlinkit kit to get CarPlay, but not taken the plunge. Lots of chat about those systems on clublexus

That's a fantastic piece of work and very kind of you to have shared it for future use. Mine isn't an F-Sport and therefore doesn't have that particular failure mode, but that's going to save someone a pretty penny at some point in future!

On the assumption that's on your 2013 GS mk4, the reverse light is one side and the fog light is the other, both LEDs as standard. Edited to add - my brother came with me to collect my car when I bought it, and piped up that he'd some bad news for me already - only one of the reverse lights was working. There is only one reverse light... so it wasn't bad news after all! I suspect yours is the same...

Forgive my curiosity - was the spare ECU functionally fine (no damaged components) but not coded to the car in some way? Hence the cloning of the data on the EEPROMs simply matching the spare ECU to the car?

Your original ones look like Denso, which is what used to be the Toyota/Lexus standard fitment. They're available from Euro Car Parts amongst other places. I find them to be efficient and silent on my GS. Can't help on the inserts, but I'd be interested to hear whether they're any good if you manage to source some and decide to take that route.

Could the solution of a Toyota part like on this thread help, perhaps? Edited to add: I know it's a different model, but if it'll physically fit, it looks like there's some adjustment room.