Thanks chaps,
West Systems is what I use for all carbon repairs, with great results!
To be honest it doesn't look like resin mixed with black colourant. When I eventually managed to get the box part off the undertray (so I could repair from the inside and make sure it was oil free) there was a "bead" of the adhesive which wasn't compressed when the two parts were originally bonded together (see attached pic). This is what makes me think it is applied with a gun. Looks exactly like the result of sealing your bath before you smooth it out. Also, the box is not a perfect fit so in places there is quite a void to fill. So whatever is used must be quite "thick" (ie not runny!) in order to not run out before it has cured.
Cheers, Neil.