So I recently purchased a 17 year old gmc pickup truck with 500,000km(310,000 miles) on it because I needed something to get to work with, I basically spent nothing on it. The only rear issue with it that I’ve found and that the previous owner disclosed is that the rear main seal has a small leak, appears to be a couple drips. The previous owner added some Lucas oil additiveto it or something like that and said it slowed the leak down a bit. So my question is how well off am I to just keep on trucking along and top my oil off when needed with some high mileage oil. I only plan on keeping this truck for a year maybe a year and a half tops till I can get the means to get something way newer and only plan on going to work and back which is a short drive.