We also offer an upgraded VITON fluoroelastomer rear seal. Viton is made by Dupont, and has much greater resistance to high temperatures than standard rubber. It also doesn't have a tendency to dry out and shrink over time while sitting, which makes it a great choice for cars which will sit for months or weeks in between being driven. Overall, Viton is considered a top of the line material to use for rear seal applications. One more way to combat those pesky rear seal leaks. These fit all big blocks, all years. Our 144-1000 kit includes both upper and lower seal halves. For installation instructions, please click on "view additional images" button above.