The drill is pretty much the same with transfer cases. Transfer cases are found on 4WD and AWD vehicles. Normally located behind the transmission or sometimes contained within the transmission itself. A transfer case splits the power coming out of the transmission and sends it to the front and rear wheels. It’s normally a self contained unit and therefore has it’s own fluid. A leaking transfer case could mean that you’ve had a seal failure but it could also mean that there is an issue inside the transfer case itself. If a bearing goes bad inside a transfer case, it could cause it’s output shaft to wobble and thus causing a leak at the oil seal. This is true for many oil leaks if I’m honest. So if you have a leak that keeps coming back after you replace a seal, you might want to verify that the part that it’s sealing against isn’t loose. If it is loose, this could be the root cause of the leak. Unless you fix the bearing or bushing problem, the component will continue to leak no matter how many new seals you throw at it. Consult your owners manual or service manual for the type of fluid your transfer case uses.