I’d switch to high milege oil and find some additive that says reduces oil leak. There is nothing in a can or bottle that will “rebuild your engine”, but there are additives that have chemicals that will “swell up” seals, thus slowing down the leaking. Understand this is not a good ‘fix’, but if you just want to get by in the most inexpensive way, without doing any major engine work, then I’d take my advice above. It will only work temporary, then eventually your leaks will come back and probably be as bad as they were before, but the doctor in a bottle might provide some temporary relief, as least enough to get the environmentalist off your back for leaking all over the ground.