I disagree with that. I've had LS's with air suspension and LS's without, and I believe the very best and smoothest ride was the LS400 without air. Even if the air system did hold air, on a car of that age it'll be on borrowed time. The fuse for the suspension on the LS430 is in the engine bay on the passenger side (right hand drive) along with various other fuses and is marked inside the cover, perhaps the 400 is the same?
The compressor that pumps the suspension is under the wheel arch cover on the opposite side.