One of the worst things that can happen to a boater on the road is an oil seal leak. A leaky trailer hub can quickly lead to an expensive towing, so make sure to take care the issue as soon as you find it. While the mechanic in this video is a bit tight-lipped, he gives a good demonstration on how to replace an oil seal. The mechanic goes a little fast at times, so we will go through it here.
After removing the tire, remove the hub by tapping it with a with a rubber mallet, spinning it as you go. Make sure to place a bin under the hub to catch the leaking oil.
Next remove the oil cap and drain it. Clean it off for further inspection. Disassemble it and inspect the seals and O-rings for damage.
Then reassemble your cleaned cap with new O-rings. Make sure the seal is secure.
Reinstall the cap to the hub with your mallet, using the tap and turn technique.
Locate and remove the drain plug. Then refill your hub with the appropriate oil.
Make sure to use a sealant on the drain plug when you replace it.
Finally, reinstall the wheel and check that your lug nuts are secure. As always, check all the parts of your hub and trailer before you start driving!