Can't you just discard the first line with your record separator, and the treat it as a normal separator?

<DATA>; # discard first line

$/ = "myrecordsep\n";

while ( <DATA> ) {
    #s{$/}{}; # get rid of your separator if you want
    print;
    print "---\n";
}
__DATA__
myrecordsep
field1=item1
field2=item2
...
myrecordsep
field1=item9
field2=item10
...
[download]

Seems (to me) to do what you want.