Vitara transfer box oil too full?

[Lincolnsteve]

Hi. Steve the newbie here. Just joined the forum today and done my introduction so now here goes with my first tech problem.

I recently got a 2 litre petrol 2007 Grand Vitara. 77,000 miles and in ok condition. I'm starting to go through the service stuff and I wanted to check the oil levels in the diffs, transfer box and gearbox.

Back diff first, no problems. Needed about 30ml to top up. All good.

Came to the transfer box and there is evidence of a very slight leak and the drain plug was a little loose. So I started to loosen the fill plug expecting to have to add a bit of oil but as it came out so did a load of oil. I very quickly put the plug back in and cleaned up the mess.

I thought you filled all these up by topping up until the oil is level with the fill hole and maybe a drop runs out. How can there be oil above the level of the hole?

I've got 2 thoughts.
1. Am I doing something really stupid and getting it wrong or
2. Is there a seal between the gearbox and the transfer box that could have failed and be over filling the transfer box from the gearbox.

I certainly hope it's just me being stupid. What do you all think?