oil leak

Hi i asked a question about my oil leak and you asked if leak was sudden
just a drip or spraying all over. I change my oil every 3 000 miles or so.
when i t has been changed he has put 5 quarts in  and only takes 4 this
time when I took for change he said me oil was very low and hardly none in
engine. no oil light came on but i did notice drips on my garage floor and
the oil pan was coated with oil when he put it on the hoist. I have been
keeping a close check on the oil and noticed that it still reads over full after
driving it for 3 weeks. when I called him he said he has been putting 5
quarts in but would not hurt anything. My book says do not overfill and also
other information says it can damage the engine so who do I believe. Now
he says may need manifold gasket or head gasket and just want to know if
overfilling of oil could cause gasket failure.