I solve the buffertank problem in another way.
Most modern bottles have the M25*2 tread.
Very difficult to find ,and expensive to buy.
I just retread the bottle with a 3/4 bsp.
And that is not difficult, nor expensive to find.
As long the tread is put in straigth, the bottle can withstand the normal rated pressure- 300 bar in most cases.
Big disadvantage, you cannot use it as a normal storage bottle anymore.