I think the mast step person was me. I just purchased an Olson 34 that showed obvious corrosion at the base of the (keel stepped) mast.
When we went to take the mast down, there was so much corrosion that the yard had a hard time getting the mast up and separated from the step. Once the mast was down, what I found was:
1) the aluminum mast step/locator was so badly corroded that it was cracking apart. I was able to purchase a new one from Rig Rite (expensive, $469)
2) the base of the mast itself had surprisingly little corrosion, and cleaned up easily with a wire brush
3) the fiberglass and oak floor stringers that the step is on top of were in great shape. No detectable rot.
4) there were some 3/8# teak pads between the top of the stringers and sitting under the aluminum step that were completely rotten. I considered replacing these with G10, or teak... but it the end decided to use 3/8" HDPE instead because I thought it would be easier to cut and shape. It seemed to work pretty well.
It's kind of an interim solution for me as I'm planning to take the mast down and paint it in a year or so. So I may revisit the G10 later.