so..........i took the M for the boot wields to be done.
when i showed him (like me) he said that it looks like only 2 had popped....but he said the main culprits are underneath the sealer.
i left him with it and went back a few hours later and he'd found 10!....yes 10! that had cracked :-o
so hes removed the old ones and replaced them and seam wielded everything else .....jobs a goodun
this cost me 130 quid.....and now i know its right...money well spent if you ask me