Thanks for replies fellas.
Engine is IO-520D
Corrosion is on outside of crank, underneath forward crankcase seal. This corrosion has been wearing away said seal causing oil leak at front of engine. This then hits the prop and gets flung everywhere. So it is not exposed to elements, not visible untill seal is removed.
Word is removal of corrosion may take crank out of limits....
Non removal may lead to failure, or at least flying around in a cloud of oil.
Engine still in warranty, so not an age problem.
Cheers