That is totally unacceptable.
Who the hell makes boilers with out testing them .
The cross tubes are inside the flue which is inside the boiler .
There is no easy fix for that
The central flue and cross tubes should be hydraulic tested before inserting in the boiler shell
They should be sending another one promptly and paying you to send the dud back
Cheers
Dennis
They've sold a lot of these, I can't understand how it wouldn't have been pressure tested.
Silver brazing should have been able to withstand even rough handling in the post.
John, I'd be asking MSM to send you a new one
whilst yours is going back you shouldn't have to have the added wait of two mailings back and forth.