Yeah that's a good shout, just happened suddenly after fluid change though which was alarming! would air need bleeding from the system or do these cars do that over time

 

You can easily remove the return line from the reservior and extend it to a container to see if there is flow through the system. That will be low pressure so it won't necessarily tell you how much pressure you have at the rack. That's why the last mechanic thought my pump was not working correctly...the pump was not visibly turbulent while running and the flow at the unhooked cooling line was not particularly strong.
I had resigned myself to drive with no power steering for a while to see if it got better over time or the problem became more obvious. Even with no assist it was only apparent below 10 or 15 mph. I didn't park anywhere tight if possible and learned how to accelerate into turns.
Fortunately I eventually stumbled on a solution, I just don't know what.

 

After reading this I think Yamae hit the nail on the head in his post #11.
If the reservoir is starving the pump that means the pump is starving the rack and pinion.
Take a look at Post #17 in this thread from tacomaworld- https://www.tacomaworld.com/threads/...esivor.322460/
I've long been suspicious the tiny screen at the bottom of the reservoir may be the root of a variety of steering issues.
I have a new reservoir ready to install on my 430 and hopefully test the theory when I can catch a warmer day. I'll report back when I do...

 

Thanks everyone for their posts. It's been really helpful. The steering has become lighter over time & driving. It now only feels weighted when making light adjustments and after running the car for an hour or so.