new engine using oil

[Lance Workman]

My 1930 roadster deluxe had an rebuilt engine with 19 miles on it when I bought it several months ago. The previous owner knew very little about
the engine work done on the engine because when he bought the car that
owner had just died and his widow was living in a different state. No info
on the engine is now available. I have about 300 miles on the car now.
I changed the oil at about 250 miles. It originally had straight 30 weight
oil in it. I replaced it with Mobil 1 10w40.
Now the car seems to use more oil. After driving about an hour the oil level on the dipstick is about 3/8th of an inch lower than when I started.
The car seems to run fine and there isn't any smoke in the exhaust. I have noticed though that there is always some oil on the side of the engine near the dipstick area of the car when I return from driving it. Originally there were a few oil drips beneath the car under the oil drain bolt but that was taken care off with a oil drain bolt gasket.
Shortly after I purchased the car a Model A owner had came to my place to show me how to start and drive the car. He indicated that the engine was
in extremely good shape and everything was "spot on" reference the timing
and carb adjustment.
The car has only overheated one time and only for a very short time. I pulled over and let it cool down. I changed the oil in it and added some anti freeze 50/50 to it and now it seems to run fine except for the oil usage.
Any ideas why it is using this amount of oil or is this common for the A's.
Thanks
Lance