They draw the LLs, so every quali last round player has the same chance.
I see now, not the same chance for every player because they mix the rankings and drawing.
2009 OFICIAL GRAND SLAM RULE BOOK
Lucky Losers shall be selected based on the computer
rankings used for the determination of qualifying seedings as
The order of the four (4) highest ranked players shall be
randomly drawn, thereafter the order shall follow the players'
rankings, unless there are more than two (2) main draw
withdrawals at the time the Qualifying competition is finished
in which case the size of the random draw will be the number of
withdrawals plus two (2).