Units used for plumbing the vent boots are usually either made of plastic only, a combination of metal and plastic or just made up of several pieces of metal. You should start by examining the plastic bases to see if you will see any sign of cracks. The metal bases should be examined to check for any sign of any damaged seams. It is also very important that you check at the material that always cover the pipe. The material is commonly referred to as the rubber boot. It is possible to find this material torn and this can allow water to find its way into your room following the pipe. To fix such challenges, it is advisable that you get another vent boot to work in the place of the worn out one. However, if you find the boot in good order and that only the nails are missing, it is just normal that you replace the nails with some rubber washered screws. These types of screws are usually used in roofing involving metallic materials. Note that, you will be forced to work on the nearing shingles on both ends. Take care when removing the shingles to avoid damaging them especially if you don’t have any plan of replacing them.