Did you replace the filter in the bottom of the fluid reservoir? Possible that it's gunked up enough to create an airlock and prevent the pump from sucking fluid? For giggles, you might pull the filter and see if you can get the pump to prime itself.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]