You need to open up your Owner's Manual (OM) and read it.
1. There is a diagram of the Dash Lights pointing each one out and explaining them.
1.a. You'll find there is no warning lights for any fluid levels, elsewhere in the OM it will talk about how to check the fluid levels in your vehicle. Most vehicles do NOT have dash lights to tell you the fluid levels and people often mistake the low oil pressure light to mean low oil level (its NOT and its indicating a much more serious problem than low oil level). Other than Washer Fluid and Fuel Level of course.
2. No, that does NOT look normal, normally you may find a little bit of wetness around the seals or plugs, but the photo looks like more than normal, would concern me and I would check the fluid level and top it off or fix the leak.
3. The OM will list a fluid change interval for the Axle's. The OM will list the proper fluid to use for the axle. You just have to open it and read it.
NOTE: many OM's set one or the other extreme for axle fluid change, normal duty - life of the vehicle, severe duty - every 15k miles (~30k Km). Normally I use the severe duty schedule for maintenance, but I don't tow or off road enough to submerge the axle in water, so I use a little common sense and pick a change interval some where in between the two extremes. Personally I change it every 30k - 50k miles.
NOTE: when checking the level for the fluid, you pop out that rubber plug, like already suggested but the proper level is actually 1/4" below the bottom of the plug, up to the bottom of the plug is generally considered acceptable (i.e. NOT overfilled). 1/4"? Stick your finger in the hole only up to the first joint and bend the tip down, if it touches oil before you've bent it down at the first joint as far as possible, you're good, if it can't touch oil, you're low on oil.
LEAK Fix? Leaking oil will drain to the lowest part of the axle before dripping off, so that bottom edge of the axle being so wet with oil can be deceiving, it might be leaking from somewhere else and NOT from the seal at the bottom of the cover like it appears, so look it over and see if its NOT actually from another source. Another area that could leak is the seal at the pinion, where it bolts to the drive shaft.
The GLUE you speak of is RTV (Room Temperature Vulcanizing) Silicone Sealant. If the leak is from between the pan and axle, you can pull it off (draining the fluid), check the pan/cover is NOT damaged and clean off the old RTV Silicone with a wire brush. Buy a new tube of RTV Silicone and follow the instructions on the package for the new RTV Silicone to reattach the cover and reseal it. Then fill with the proper fluid.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.