You're already tasting that drink you're going to have to celebrate your successful drivetrain rebuild. Once you screw the differential cover back on the job is done and you can relax. Just then, you drop one of the differential cover bolts and even though you catch it, it slips out of your greasy fingers, bounces and then rolls right between the slats of the drainage grate in the shop floor. You can hear it echo down the pipe as it falls out of your reach. Never fear - 4WD sells replacement differential cover bolts for as low as $2.99.