  The historical microlensing surveys MACHO, EROS, MOA and OGLE (hereafter
summarized in the MEMO acronym) have searched for microlensing toward the LMC
for a total duration of 27 years. We have studied the potential of joining all
databases to search for very heavy objects producing several year duration
events. We show that a combined systematic search for microlensing should
detect of the order of 10 events due to $100M_\odot$ black holes, that were not
detectable by the individual surveys, if these objects have a major
contribution to the Milky-Way halo. Assuming that a common analysis is
feasible, i.e. that the difficulties due to the use of different passbands can
be overcome, we show that the sensitivity of such an analysis should allow one
to quantify the Galactic black hole component.
