Trying to remember a uni lecture, Comet wing sPAR

I have just seen a read some of the other Comet thread and it brought to mind one of the mech eng lectures at UMIST which mentioned a metalurigical problem in wing spars, I think this was on the Comet.

I remember the main spar of the aircraft concerned was an aluminium? forging which then had a singnificant groove machined in part of it, my recollection is that condenstion collected in this groove and the metal’s grain structure caused abnormal? corrosion problems.

Is my memory correct?