  The diverse massive stellar population in the young massive cluster
Westerlund 1 (Wd~1) provides an ideal laboratory to observe and constrain
mass-loss processes throughout the transitional phase of massive star
evolution. A set of high sensitivity radio observations of Wd~1 leads to the
detection of 18 cluster members, a sample dominated by cool hypergiants, but
with detections among hotter OB supergiants and WR stars. Here the diverse
radio properties of the detected sample are briefly described. The mass-loss
rates of the detected objects are surprisingly similar across the whole
transitional phase of massive star evolution, at ~10^-5 solar masses per year.
Such as rate is insufficient to strip away the H-rich mantle in a massive star
lifetime, unless the stars go through a period of enhanced mass-loss. The radio
luminous star W9 provides an example of such an object, with evidence for two
eras of mass-loss with rates of ~10^-4 solar masses per year.
