after I change the oil in my car It started making a knocking sound It has a front and rear main seal leak But I've kept it up And I've had Lucas in it

Sounds like your engine may be nearing it's life. As a last resort, checkout Wynn's Engine Restore and an Oil Treatment as additives. Sometimes they work, sometimes they don't. In the long run, you will need to have your engine rebuilt or replaced.

get a broom handle or a long screw driver and put it up to your ear and then place the other end on the oil pan...front crank area...isolate the noise before you start to freak out...