Ohh!

Whilst I appreciate that on auction site what you see is what you get, but, i did not expect this. Not a problem as I have a few spares, the question is this, is it due to mis-use of the stove or general wear and tear?

 

underburn

 

I reckon the only way that the hole could grow so large is the cap was used with a 'sacrificial ' coin (or similar) on top of it.... in an underburning situation.
nick

 

Let me gander a Guess...someone used a torch to clean out the carbon in the tubes and
Mike

 

It would of been hot enough to keep the flame burning straight up through the tube.
Time to learn sil brazing

 

Definitely it is due to underburn usage.