A loose, leaky or damaged oil drain plug can cause unsightly stains on your driveway, as well as reducing the amount of oil in your engine. The leak should be addressed promptly. The last thing you want is for the plug to fail completely and unexpectedly dump all your oil out. This can cause irreparable damage to you car's engine, which will cost you a lot more than fixing the plug.
Engage the emergency brake, place the car in gear and chock the tires with blocks in front of and behind the tires to keep the car from rolling. If there is insufficient clearance to access the oil drain plug, you may also have to jack up the front of the car. In that case, chock the back tires and place sturdy jack stands under the support areas, as recommended by your car's manual.
Align the oil pan under the drain plug to protect against leakage.
Turn the oil drain plug counterclockwise with the adjustable wrench. If it turns easily, the plug may be loose and simply require tightening. If unscrewing the plug takes effort, then the plug was probably tight, but the washer has failed.
Remove the drain plug and replace the washer. Keep in mind that the oil in the car will drain completely when you remove the plug, so make sure the oil pan is properly aligned under the hole. Replacing the washer should be a simple matter of pulling one off and sliding on the other one. In some cases, the entire oil drain plug may need replacing to change the washer.
Screw in the oil drain plug and tighten it up against the oil pan. Be careful not to over-tighten; you only need to snug it up. The oil pan is likely made of thin aluminium and will strip very easily. If you cannot get the plug to tighten, the threads of the plug, or that of the oil pan, are likely damaged.
Remove the oil drain plug again and inspect the threads. If the threads are flattened, smooth or non-existent, the drain plug is damaged and should be replaced with a new one. If the threads look good, the problem is in the oil pan. You can replace the oil pan, or purchase a self-tapping oil drain plug of a slightly larger size.
Screw the self-tapping oil drain plug into the hole. You may need to repeatedly screw it in a little ways, back out and clean the threads to remove displaced aluminium that was chiselled out by the tap. Depending on the plug and the oil pan, you may need to drill the drain hole first to allow the self-tapping drain plug to fit and tap into the hole.
Snug the plug against the oil pan and wipe off any residual oil. Since the oil is already drained, you may as well replace the filter and refill the engine with fresh oil to save yourself the trouble of changing the oil later. Inspect the oil plug carefully and verify there is no leak.