Most likely the rear main seal but could be the tranny.  Is it auto or 4 speed?

Thank you. My Vette is automatic I noticed that oil drops when hot. When the car is cold no drops are falling (if I leave the car not running two or more days, no new oli spots are presente under the car). Bye

You may also want to check along the bottom edge of the valve covers for leaking valve cover gaskets.

Is it engine oil or transmission fluid?  They are different.  Tranny fluid is usually redish.

After checking there is no leaking valve cover gaskets. Thank you

The fluid is dark brown / black. It has to be engine oil. Today I used the car, about 50 miles, after 2 days of stopping. No new spots on the ground when I start to drive. When I was back home, waiting the garage door to open, some drops of "fluid" were on the ground in the place the car was waiting. Next week I will lift the car and I will look under. I think I will give you new material... For now, thank you!

Thats just how it goes with any old vehicle, the seals just get old especially if that car sat for two years.  Drive it and enjoy it for the driving months and tear the old girl down in the winter months

my 73 was leaking at the cork Valve cover gasket - went with rubber -fixed

did you fix your horn problem? If you didn't the horn relay is tucked in the fender on a 73 by the master cylinder