I had that problem with my 57 T-Bird. If I let it sit for too long, the torque converter leaks down and ford-o-matic thinks it has too much fluid in it, and starts burping it out the dipstick. At least that's what I was told. I start her up run through all the gears. Basically take if for a little run. Since I started doing that, no more problems. I was told that there was a tech bulletin that stated that the T-Birds should not be allowed to sit for extended periods of time or this problem would occur.
Hope this helps.
Bill Poland312 V8 - in a 1957 T-Bird
Baltimore, Maryland