I had heard of Denso spark plugs that shed their iridium center
elctrode.
I had that happen with a Denso IK20.
I swapped to NGKs,two heat ranges colder.
Good color,gapped down to .028,the car loves
them and the performance and mileage are great.
Thank goodness it appears that the electrode
pooped itself into the exhaust or hopefully retired
to a quiet and safe corner for the duration.
1991 318i,150K bone stock.