Golf Mk5 Gti - Cap Missing in engine bay?

[Mooks]

Checking the engine this morning I noticed that the is a hole, looks like a cap missing and you can see something rotating I presume it might be a clutch inspection cap. Should there be a cap over this hole?? If yes, does anyone know the part number so I can replace it if its missing.

[the-photographer]

I would post this over on http://www.mk5golfgti.co.uk/forum/index.php/board,...