Removal of Headers

[Dustydes]

Can take quite a bit of tapping flanges and wiggling to get free.
The corrosion after removal might have to be chiselled out of recess with screw driver etc to get it clean for refit.
You can also replace with stainless bolts.
And before anyone starts shouting about electrolysis/corrosion problems, if you use a thread sealant and coat studs well you will not get this problem. 
Don't forget new copper compression washers.


Good luck