What do the markings 40/100/56/B mean on this capacitor?
That is the climatic category data for your capacitor.
Your capacitor is rated from -40 to +110 degrees C.  The 56 means that your capacitor will be OK if operated at 95% humidity and 40 degrees C for 56 days.
The &quot;B&quot; might be the flammability rating, as described in this document from Vishay (see page 5.)
Given that you mention a steam iron, I think you'd be better off finding capacitors with the same climatic rating as the original.

That capacitor is a safety capacitor - that's the &quot;X2&quot; marking.
Make sure that any replacement is also rated X2 and also has the same voltage rating as the original.