Mark

im not sure about it binding with oxidation, you should call SWS on that, but I know how to easily get it off.

i use our gutter cleaner/hydroxide based product and put it in a hose end sprayer. Coat the siding, let dwell for a few minutes and rinse heavily. I have never had to agitate the siding using this method. I am sure OxiWash works but have never tried it.

Mark,

Sounds like damage you uncovered instead of damage you caused.  Oxidation takes years to appear heavily.  You just cleaned the gunk off the surface of the oxidation/damage, exposing the existing damage beneath.  She can't blame you for "exposing" pre-existing damage, and it is absurd for her to expect you to pay for the restoration that was necessary before you started the work.  She's noticing the damage more now because she is looking at the siding more critically than she did before, inspecting the fine details that she didn't really pay attention to before.  

From what use I've had with Final Wash, I've never noticed any kind of binding like you are talking about.

Mark,

we use a few different gutter brighteners. gutter Granade and BD 200 are pretty much a staple on the trucks. SWS sells Oxiwash

i use the BD 200 more the rest because it seems to work on all gutters and has a better working capacity in the cooler months of the season. It is of course more caustic also.