Works for me (assuming you meant a #! at the start of y.pl); try adding this to the top of y.pl:

print "private x ", (-f "/u/myself/somescrap/x.pm" ? "exists" : "doesn
+'t exist"), "\n";
print "dir: $_\n" for @INC;
print "$_ found at $INC{$_}\n" for keys %INC;
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and see if it shows anything useful.

There's no way Config being used by a module that x uses could influence where x is found; x is already loaded at that point.