If your sample data is representative, line terminator appears to be eol[0-9]' (or, maybe +eol\d+').

Looking from that angle, might it be easier to substitute on the (apparently unambiguous) +eol\d'
update: belated example:

#!usr/bin/perl -w

$foo = <DATA>;

$foo =~ s/\+eol\d'/\n/g;
    print $foo;


print "\n\n Done\n";

__DATA__
AAA+XXXX+1234++here?'s some text+eol1'BBB+XXXX+1234++here?'s some text
++eol2'CCC+XXXX+1234++here?'s some text+eol3'etc.
[download]

# OUTPUT:
#
# AAA+XXXX+1234++here?'s some text
# BBB+XXXX+1234++here?'s some text
# CCC+XXXX+1234++here?'s some text
# etc.
# 
#  Done

The following notion is mine, and may not be wise (CORRECTIVE comments welcome!):
It's usually worthwhile to match against the largest possible chunk of data, to minimize ambiguity for the regex.

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