<VV> Diff Fluid Level

[John & Sandy]

I have a '65 Corsa Turbo with a 4 Speed.  When the car sits with the motor NOT running, the Differential dipstick reads 3/4 full.  When I start and run the car, the dipstick shows NO Fluid.  Is the fluid low?  Should I add more or rely on the cold reading?  My other 4 speed is a '66 put into a '65 convertible.  I check the fluid level under the car, not running.  Thanks, ahead of time,  for any advice.    

John Johnson
'64 Monza Conv PG
'65 Corsa Conv 140 ('66 4 speed)
'65 Corsa Turbo Coupe ('65 4 speed)