"Is there a way to manually set the SLS height, so at least it'll ride at a normal height? Isn't there a 'normal' setting on the SLS valve, where the hole in the valve arm and the valve assembly are aligned?"

In short no. The sls valve operates by changing the amount of fluid in the struts/accumulators. It does this in response to the ride height. If you leave the valve in the fill position, you will get the high pressure noise and ride height that you have observed. leave it in the off position, and you experience the sagging. I really think that you should start by replacing the accumulators, and alleviate your harsh ride. After that, you will be better able to diagnose the valve operation. Or, just rebuild the valve while you've got it apart for piece of mind, either way, I think a set of accumulators is in your future.

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