98 Explorer Transfer Case

I have a 98 Explorer that has the 4WD Hi and Lo lights flashing.
While I've read messages stating that this could be caused by
dirty speed sensors, I happened to notice when I was under
the vehicle that it looks like there has been a bit of fluid that
has leaked out of the transfer case (at least I think its the
transfer case, I'm not sure).

My questions:
1.) Since I am unfamiliar, what does the transfer case look like?
2.) Is there any way to check the fluid level?
3.) If there is a leak, is there a way for me to fix the seal myself?

Thanks in advance.

The transfer case is just before the rear driveshaft. The rear shaft seal is probably leaking. This part is about $8 and is fairly easy to replace. Remove driveshaft and remove center nut. The flange will pull out, a jaw puller will help. The seal can then be pryed out with a screwdriver. Polish the shaft with very fine sandpaper and oil.

The 4WD has a wet clutch and when fluid gets low these stick. This is likely your problem with flashing lights. Drain and refill with Mercon. On the back of the casr there are two plugs which accept a 3/8 extension socket. less than 2 quarts. Wouldn't worry about the snsors. These do not collect magnetic particles like the older ones do. Disconnect battery after new fluid and this will reset the flashing.

Bad news. With driveshaft removed or in neutral, lift up on the drive shaft. It should not move. A number of transfer cases are experiencing bearing mount wear. This causes rear seal leaking. Only solution is new half case.