Hopefully just an old gasket.

'73 Root Beer said

Been a good car owner, and only owning the car for less than 5k miles. I have been checking oil every 500 miles. Today...milk on the stick. I am hopeful it is only a gasket on a 40 year old 318 with 80k miles. Pray for Root Beer, she needs kind thoughts right now.

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I have had alot of 318 from that era.
Most likely just condensation in the motor, how much do you drive the car every time you start it up?
Change the oil, clean the breathers on the valve covers and make sure you run it everytime you start it up full operating temperature.
20 minuates is the minimum time I run all my antiques, when I start them up, drive it every time to keep everything lubricated.

Does the bottom of the dipstick have about 1/2" of milk and the rest looks clean, then you are dealing with condensation.