There is a tendency for muck to fall through the hole in the auger deck and thence through the seal and into the gear box, see the picture below. There is now a seal available which attaches to the bottom of the auger drive dog, see photos above. The later dogs have a shoulder on the bottom for the seal to attach to. It's not difficult to reproduce this shoulder if you have a lathe, just weld a suitable size washer to the bottom of the dog and then turn to size. We can advise 01609 773607. With or without these seals it is very important to check the oil level and color frequently and top up or change as required.
The first pic is an auger gear box with dog and seal fitted. The second, from left to right, shows a new type dog with shoulder, a new type dog with seal fitted and an old type dog. The next two pics are closer views of the second.
We accept no responsibility for any problems you may incur by following this advice.