Funny splits / pierce throughs in the mast

[higgs]

If Ross is correct, and he may well be right, the mast should not be compromised.

 

[Ross]

If the edges of the slots are ragged and show a granular structure then the cause is probably corrosion. If there is great concern about crack propagation then a stop hole drilled at each end of the slot will distribute the stresses. It is possible to initiate corrosion on aluminum with a graphite pencil mark.
I doubt that the slots were deliberately made.