I've gained lots of great knowledge from this forum over the years, especially in repairs.
Thought this was worth sharing.

Instead of walking you through a long winded story taking months while performing two flushes and replacing two pumps, I'll quickly cut through the chase and say if you're power steering pump is making any kind of noise, I can bet you pretty fair odds that your Reservoir Tank has a clogged filter, which is starving your pump. A flush won't help you fully, nor any Lucas type additive you're thinking of doing.

If you have noise, then I strongly suggest you flush your system and immediately replace your Reservoir. Adding an inline filter to your return hose would best prevent future issues.
To prove my theory, I cut in half my old reservoir. The debris you see in the housing is simply plastic bits from my cutting tool. The important observation is the filter that sits between the two halves. Once I replaced the reservoir, my engine compartment has been it's quietest I can remember in a very long time.

 

Thanks for the tip.

Chris