How to repair a flush pipe?

I have a toilet with a low level cistern which has a small flush pipe as well as the main downpipe, I noticed a wet patch around the base of the toilet & then investigated further (all the cistern workings including pipes are encased in a wooden shroud), anyway it looks as if the smaller flush pipe has a "dripping" leak, this is dripping onto the bigger pipe and then onto the floor. Given the very limited view i have I can't seem to see water coming from anywhere else.

Bearing in mind that i have no plumbing expereince and that I'll have to work out how to take the shroud apart first, what's my best course of action with regards to fixing the problem & what I'll need to buy..

If possible please can you provide step by step info.

Any help etc would be greatly appreciated.

Regards

Dave