The rear crank oil seal actually seals on a spigot extending from the Centa outer. There are two potential problems, there are often marks on this spigot from the chuck when the assembly was machined, and its diameter is 50mm whereas the seal is for a 2 inch shaft (50.8mm). The way to fix this is obviously a new seal and install a Speedy sleeve on the spigot. Speedy sleeves are used to repair damaged shafts and will also increase the diameter slightly, although not up to 2 inches.
