Gearbox Noises & Oil

Recently in the last few days the gearbox in my SWB SIII seems to be making a lot more noise. The noise increases with acceleration and sounds like very noisy gears rotating.

Is this a lack of lubrication in the box?

If so is there a way to check it or do I have to go through the whole process of draining and refilling?

If not any advice?

PS, pretty sure that it hasn't had oils changed recently, but the last few years it hasn't done many miles at all.

Probably should be changed anyway.

you can check by taking the level plugs out and sticking your little finger in the hole.

Shall go and check that now then