Toilets, Sinks, Showers, Tubs and Disposals - Symmons-Temptrol Model A diverter spindle

To repair a leak from the diverter (the plumbing is apparently set 1/2" too far back in the wall, so the water dripped into the bathroom ceiling below, which is a different problem) I have disassembled the fixture and am waiting for the part. This is the second time I have done this three years and both times had an amazingly difficult time removing the spindle. I shone a flashlight into the pipe and noticed a fair amount of corrosion, (green, pitted) which is why the spindle was so stuck. And yes I have well water and yes it is hard. I just hope this is not indicative of what all my plumbing looks like.

I have brushed the inside of the pipe with a fitting brush. Is there any else I can do to minimize the corrosion to put off replacing the whole thing, which would involve hiring a small monkey with plumbing skills to curl up in cabinet to cut a hole in the wall. Was brushing the pipe a bad move? I bought plumber's grease to slather the spindle with when I get it.