HI ROB . I THINK I MAY HAVE THE SAME PROBLEM AS YOU HAVE WITH MY C15
A NEW GASKET BLEW .IN LES THAN FIFTY MILES
IVE GOT SOME SHEET BRASS .AND IM GOING TO DOUBLE UP .N MAKE ANOTHER GASKET
TO SLIP UNDERNEATH
IVE MADE MANY GASKETS OVER THE YEARS
IF THE BRASS IS NICE AND SOFT YOU CAN PUNCH THE HEAD BOLT HOLES OUT BY USEING A SMALL SOCKET ON A FLAT
SURFACE AND TAP WITH A COPPER HAMMER .
AND CUT IT OUT CAREFULLY WITH TINSNIPS
HOPE THIS HELPS.AND GOOD LUCK