Before I bolt up my transfer case I would like to replace the seals. While looking up front seals I noticed R-Auto have a double lip seal and different shaft sizes. Has anyone used this double lip seal? Is there a way to tell what shaft I have or do I have to mic it? Also I noticed that the rear seals come in either a rubber coated seal or nitrile. Is one better than the other? If there is anything else I should know before throwing this thing back in let me know. Thanks