Rear out put shim and bearing replacement ?

I have a 1959 CJ 5 and my dana 18 rear transfer output shaft oil seal is starting to leak and I have a vibration in the transfer when I am coasting. With pressure on gas or off it is smooth. Just in that no load spot on the drive train is when it vibrates. I do have some play in the out put shaft up and down. This has had it since it was rebuilt.
So my question is can I change out the bearing or just shim the bearing while in the jeep or do I have to pull transfer out to do that.

Thanks
John