J,
Since you appear to be unaware of the necessity to tell us about
which replacement diaphragm you used (?), I must conclude that your problem actually stems from this over-sight ( & everything that follows from thinking
"type" > "just doesn't matter" ).
ie; Cheap chinese junk, won't cut-it ( no matter the impedance stated, or price paid ).
The only replacement diaphragms that can be considered "proper" replacements for your Flamencos, come from
GPA .
Match the dcr's of new ( to old ) diaphragms.