Speedometer not working. 71 Blazer

[NJKelly]

Hi guys. I've looked at some videos on pulling the speedometer cable out of the transfer case and then spining it to see if the needle moves on hlspeedometer. I'm unsure if by removing there will be oil leaking all over the place. I'm fine with that but I obviously need to replace that oil and don't know where in the transfer case you do that but I'm sure that's on the internet. Just don't want to start it without knowing if oil will leak, thanks. Believe it's an np205.