Snapped stud on ecoMAX 835e heat exchanger. Repair or Replace??

I've found a problem, caused by a perished gasket that caused a securing bolt to be overheated and shear on the front flange plate that holds the burner. There are 5 studs in total, they appear to be either welded or pressed into the main body of the heat exchanger body. The snapped stud is the one that also supports the air pipe and has about 6mm of the stud remaining, just enough for it to be flush with the face of the flange plate when fitted. I suspect everything is stainless steel. I’m just wondering if anyone has had experience of this and if there are any repairs specific to this model that can be carried out to avoid the £400 cost of a replacement part.