check and make sure the oil drain plug has a coper washer not a paper,rubber or felt one!

if you don't have the copper washer it will probably leak no matter how tight,

secondly check seals at the front and back of the oil pan. Sometimes the oil can seep from the head if the head needs tightening. If it's leaking out of the bell housing area you may need a rear main seal.

1 qt of oil every 1000 miles is about the most oil anything in good condition should use.