  Since 2013 we are performing with the Nancay Radio Telescope (NRT) a
monitoring program of >100 Galactic disk OH/IR stars, having bright 1612-MHz OH
maser emission. The variations of the maser emission are used to probe the
underlying stellar variability. We wish to understand how the large-amplitude
variations are lost during the AGB - post-AGB transition. The fading out of
pulsations with steadily declining amplitudes seems to be a viable process.
