  We re-analyze the M31 microlensing event WeCAPP-GL1/Point-AGAPE-S3 taking
into account that stars are not point-like but extended. We show that the
finite size of stars can dramatically change the self-lensing eventrate and
(less dramatically) also the halo lensing eventrate, if events are as bright as
WeCAPP-GL1. The brightness of the brightest events mostly depends on the source
sizes and fluxes and on the distance distribution of sources and lenses and
therefore can be used as a sensitive discriminator between halo-lensing and
self-lensing events, provided the stellar population mix of source stars is
known well enough. Using a realistic model for the 3D-light distribution,
stellar population and extinction of M31, we show that an event like WeCAPP-GL1
is very unlikely to be caused by self-lensing. In the entire WeCAPP-field
($17.2'\times 17.2'$ centered on the bulge) we expect only one self-lensing
event every 49 years with the approximate parameters of WeCAPP-GL1 (time-scale
1-3d, $R$ flux-excess <19.0 mag). If we assume only 20% of the dark halos of
M31 and the Milky-Way consist of 1 solar mass MACHOs an event like WeCAPP-GL1
would occur every 10 years. Further more, if one uses position, FWHM time
scale, flux excess and color of WeCAPP-GL1, self-lensing is even 13 times less
likely than lensing by a MACHO, if MACHOs contribute 20% to the total halo mass
and have masses in the range of 0.1 to 4 solar masses. We also demonstrate that
(i) the brightness distribution of events in general is a good discriminator
between self and halo lensing (ii) the time-scale distribution is a good
discriminator if the MACHO mass is larger than 0.5 solar masses. Future surveys
of M31 like PAndromeda (Pan-STARRS 1) should be able to provide many more such
events within the next 4 years.
