This is behavior I've never seen before.

Possible causes?
Low cells in car battery (replacing this weekend w/ VW battery before winter), debris in power steering reservoir, failing power steering pump, air in power steering fluid system, 605 Servotronic relay failure?

Would a failing 605 Servotronic Relay cause intermittent power steering issues. The power steering is good most of the time, but goes in and out. The cells on my battery are pretty weak so I'm changing the battery this weekend. Would reduced power caused by a loose belt or poor battery influence the variable-assist power steering behavior?

When I am driving it will drive fine, but a lower speeds go to make the turn and power steering diminishes suddenly requiring manual strength, then comes back in. Power steering fluid levels full, perhaps debris in the power steering fluid reservoir creating vacuum loss?