I recently acquired a 2004 Hyundai Santa Fe GLS 3.5L 6 cylinder with 155,000. There is a small oil leak on the garage floor which i noticed. I brought the car to a Hyundai dealership for a diagnosis of what the oil leak may be about. The diagnosis showed that there was oil leaking from the valve cover gaskets and the transfer case. The dealer advised replacing the seals on the transfer case but if it continued leaking the entire transfer case would need to be replaced for $2400 at the dealer. I have gotten an estimate to replace the seals at an auto repair shop for around $800 parts and labor with no guarantee that the oil leak issue will be resolved and need to replace the entire transfer case. I am wondering if it would be more cost effective to have an auto repair shop replace the leaking transfer case first with a rebuilt transfer case rather than taking a chance on spending $800 to repair the seals which may or may not resolve the oil leak and I wind up putting in a new transfer case anyway after spending $800 to replace the seals.
I’m a little surprised you would buy a high mileage Hyundai/Kia after being on this forum for a while…
Anyway, I would find a shop that is willing to clean the t-case up really good and maybe even add a little dye to the fluid and have you drive it for a few days or a week and bring it back to find the leak instead of just guessing…
You can not always find a slow leak on a vehicle right off the bat, the air blowing around at 60-70 mph, can blow oil in places that it is not leaking…
Or you crawl all over it cleaning the case with brake cleaner or whatever and drive it a little bit and look for leaks yourself…
Since the valve cover gaskets are probably the least expensive, & you don’t know which is the main source of the leak, hire a shop to replace the valve cover gaskets first and see how much the leak is reduced. It might be enough of a reduction that placing something under the car to catch the remaining oil drips is good enough.
If this experiment shows the xfer case is the main leak source, I’d start with the idea DMP proposes above, clean it up, add dye, to see exactly what on the xfer case is leaking.
Be sure to keep a weather eye on the fluid levels & top off as required, until the leaks are resolved.