You may now use the MODs sectioon in the control panel to update your source mod to the latest version.
Update Details:
# Fixed support for many updated games (CS:S, DoD:S, TF2, HL2DM, L4D, L4D2, Garry's Mod)
# Added support for Alien Swarm, Firearms: Source, and Fistful of Frags
# Bug fixes and a few new TF2 developer features
