I have a bad seal in my d4d 83j .. transmission group 4s8686. Looking to buy good used unit or any information that anyone can help me.. id appreciate it. My trans rangement number is 5s4499.. im looking at a transmission group no 4s8686 with an arrangement number of 4s8665. I know arrangement matters. It comes from a 951b. , sn 86j, but would this work in my d4d? Does anyone know what the differences might be? Thanks in advance.  

Cat will usually have the seals. Also try 

  Machinery Trader
Great place for parts
Good luck