Hello Peter,
Thank you, regarding LED lights, yes they are totally waterproof, all sealed, comes with new grommets to pass harness through body work. For the Aristo is was just plug and play.
For the GS300 I'm sure you have to do a simple wiring alteration as there are only 5 wires in the GS300 Harness. It has been posted on here by someone else,along with instructions how to replace rear lights.
I checked this out first and found it very usefull, well detailed with photos.
As for the bulb failure error in the dash I can't really comment, as the warning bulb has been taken out some time ago. I was told the reason for this is that due to the fog light modification done on vehicle to comply with MOT/british requirements it caused the bulb failure light to come on.
regards
Paul.