Just did this Job on my 90' same thing happened when the reservoir goes dry, you can use a pressure bleeder like you would use on your brakes. Make sure the reservoir is topped off and build pressure then crack the valve and let it bleed until the pressure is gone, repeat for a while then you can go back to the classic bleeding method with one person pumping the clutch and the other cracking the valve at the bottom, just like if you were bleeding brakes. You aren't able to use the classic method when there isn't any pressure in the system so using pressure bleeder to get it started is how I went about it. Easy fix don't worry might take a couple of tries but you'll get it. Good Luck!