route -f and file sharing over wan links

The Symptoms:

Clients over routed connections periodically loose access to file shares on
a W2k3 DC, but do no loose access to other file servers or exchange servers.

Clients on local LAN do not loose access at all.

Running the route -f command on the w2k3 DC server followed by re-instating
default route returns access for approximately 30 minutes.

Rebooting the server returns access for a longer period of time (12 hours)

Question:
Has anyone experienced this behaviour?