Re: Survey found corrosion in mast
Typical problem, and yes that is a typical cure. As long as it is done properly (strong & keeps alignment and mast height) cutting off the bottom of the mast--clean and level--and putting a step under it is nothing new and nothing to worry about. And if the new mast step is fabricated properly, with some weep holes, the problem won't recur.
HOWEVER, it does mean taking down the mast and doing some work, and that should mean a substantial price adjustment to reflect the job.
At the same time you might want to rerig the standing rigging, since the mast will be down anyhow.