There can be some nasty responses on this forum. A cracked bushing is a bad thing but it doesn't necessarily mean a catastrophic failure. It simply means that you MUST get it repaired asap UNLESS you're told NOW.

LS430 really is the best Lexus ever made. I was just at the Lexuas dealer and I was told that Lexus tech's believe it was the heyday and best Lexus ever built for every day use. Not even the LS460 holds up to it. The quote: "They're not built like that any more."

 

Nah. A cracked lower control arm bushing isn't anything to sweat. If its holding its shape, it's drivable. And if OP's going to change the entire lower control arm, then the 'sympathetic' wear on the first lower control arm bushing isn't much to worry about. And OP lives in sunny south cali, OP's parts are probably in much better condition than components in cars with comparable milage that see winter.

Regarding the diagnosis - do you have an OBD reader? The cat might be fine, the engine coolant temperature sensor could be out and the car could be running rich and heating up the cats too much. It's possible you haven't ruined anything yet, but I'd have a Toyota specialist check it out. You should see coolant temperatures of around 178-188 degrees F on the freeway. The engine temperature gauge on the dash can't be used check the engine coolant temperature sensor (the ECU and dash read from different units).

The transmission fluid level is probably fine - and if it's leaking it's leaking. I think low fluid levels manifest first in issues with reverse (typically a clunk) but that's just based on issues with the 4 speed transmissions. The 5 speed is just a little too rare for me to find many accounts of cars with low fluid levels.

And don't be too worried about burning oil. A quart in 5000 miles is a little higher than ideal, but consider running a quality synthetic like Mobil 1 Extended Performance or high milage. You might also get away with a 40 weight oil. There might be a leak in the valve cover gaskets, but maybe not. I personally wouldn't sweat it, or I'd get used oil analysis done to check the condition of the oil. High milage aluminum block engines burn oil. It happens. Just check the oil level every few tanks of gas.
Anecdotally Marvel Mystery Oil is good at cleaning engines but terrible for oil. I ran it in one of my older motorcycles and it cleaned the varnish off one part, but it sheared in 500 miles (normally oil doesn't shear until 4k miles in that particular motorcycle).

I hope the LS is everything you've been looking for. IIRC from Tumblr your old car was a Honda Fit? ( I have an unpublishable name on it but I posted a picture of my cat on a wall of text) They're both great. But the LS is superlative (at least in this price range) and it's a study in the state-of-the-art. It's so smooth and effortless and long lasting. I don't know if it was THE best Toyota, but it's among the best and that's some heady competition.

Good luck!