it by simply tightening the bolts (in the proper sequence), but sometimes you need a new gasket. do you notice a loss of oil with no leaks? say 1-quart every 1500-3000 miles?
follow the pictures below for the location and proper tightening sequence. most should be able to solve the problem by simple tightening, but some may need to replace the entire gasket as it may be shot. make sure you follow the sequence for tightening! 