An engine flush is corrosive to seals as was said, but the main problem is that when you drain your sump, you are usually left with about half a pint of oil in the bottom of it. Then a little of the flush is always around your engine, doing damage.
If you are going to use one, either take the sump off and clean out the bottom of it or use one of those suction jobs to empty it.
Not worth while to flush it at 58K, no harm in removing the sump to clear it out but.