I finally had my first major issue with the starter going out on my LS. Upon start up it's making some grinding noises and taking longer than normal to start. I just ordered a Denso rebuild starter and reviewed the process of removing the intake manifold through the guides below. Any additional advice/recommendations would be helpful.

Also since, my LS has over 230k I was wondering if it's a good idea to also replace the Knock Sensors, while I have the intake manifold off. I've never encountered any CEL codes or hesitation in throttle response and it's been running smooth. I've noticed a few OEM Genuine Denso Knock Sensors on eBay for around $45-$50 (didn't know if these are actually Denso, since the Lexus dealership wants close to over $200 for each).

A fellow member (dmgray50) did provide the following advice to replace the starter on a GS400, which I read is very similar.

1. The entire intake manifold should be removed with the throttle body. It can be done and does not require you to pull them apart. Yes, there is a hose on the bottom side of the throttle body that you may have some fun getting too, but
its was worth it to me to not have to disassemble it from the intake manifold. The other tube that comes from the side of the thermostat housing to the underside of the throttle body is holding antifreeze. Pull off and plug with something. Its not a big leaker in general, less than a quarter cup at most. I plugged it with an ear plug.
2. You do not need to drain the radiator at all. Totally unnecessary step.
3. You will need to have the following special tools: long needle nose pliers, a swivel head box end ratchet wrench - 14mm, Flarenut wrench for the fuel line. Do not attempt to undo that without one. You will probably destroy the fitting.
Of course you will need the 3/8 ratchet, universal joint, 10mm socket, 12mm socket, 14 mm socket, minimum of 6" extension, breaker bar possibly for starter bolts. The swivel head box wrench is needed for one starter bolt. Using that tool will
then enable you to not remove the coolant bridge in the rear over the starter. WIth that wrench, it will save you an hour alone.
4. You must vacuum out the intake area after removal of the manifold. All the old wire heat wrap will drop down all over your open manifold very easily. This is probably the most important part of doing this, Take very special attention to getting all
the dirt, debris and tape out of this area before reinstallation. Taping over the manifold is highly recommended after cleaning it all out.
5. When reinstalling the starter, recommend getting both 14 mm bolts as tight as you can, hit the back of the starter with a soft mallet to make sure its absolutely flush with the mount. Then tighten to spec.
6. There is the coolant temperature sensor located very close to the front corner passenger side of the intake manifold. Be very careful of that when reinstalling the manifold. Easily breakable when putting it back in. Yes, I did it and thankfully its a local pickup part at any auto store.
7. Torque the manifold down very carefully. hand tighten them all, then go back and start at the middle working out on the bolts, 14 lbs I believe was the spec.

Youtube Link for GS400 Starter Replacement

 

I wouldn't replace them. Once you've had the intake off once you will see that it's not that difficult to do again should the need arise. I could probably have mine off in about 45 minutes now that I've done it. The hardest part for me was unplugging all of the connectors. My fingers were sore for a few days after. A few other things to know:
The bolts holding the intake on are T45 torx.
Remove the throttle body first and then disconnect the small coolant line underneath that is hard to get to.
Give yourself as much slack in the wiring as possible because the intake has to go upwards quite a bit so the vacuum tank on the bottom will clear the china rail.
With your mileage you might want to separate the upper and lower intake after it is removed to clean out any accumulated oil. You'll need a new gasket. I would also recommend replacing all of the injector o-rings and seals as well as the pulsation damper crush washers while you have the fuel rail off. My injector seals were very brittle at 114k miles.
I posted a few intake pics in my blown head gasket thread. https://www.clublexus.com/forums/ls-3rd-gen-2001-2006/812606-blown-head-gasket.html