Leaking gearbox, but where from?

[Gingerbread Man]

I've a Caterham 6 speed gearbox. The below image is of the speedo drive output, but what but is leaking? Has a seal buggered up? Annoying as it was only rebuilt late last year. There is play where the drive goes in and is secured by a circlip. This appears to be where oil is shown.

Can I jack it back up, lay on my back and fix the issue, or is this going to be a pain?

[Gingerbread Man]

Tray underneath, circlip off, whip the drive out, the seal out, new one in, drive in, circlip in. Then top back up, or should I drain the whole lot first? Could jack the car up on one side only?

[Gingerbread Man]

I'm used to doing things 'live' as a plumber. I'll get one ordered, see how long it takes to arrive.

So that fits the 6 speed. Mentions other gearboxes, but is the Caterham 6 a modified Ford gearbox?

[Gingerbread Man]

I've asked my local Ford dealer. I'm in Oz, but the questions been asked.