Bath leaking

[MaxP779]

Help me ocuk DIY experts! Theres a leak in my bath, I think ive located the cause but im not sure, not sure what to do either.

This is underneath the bath, the leak seems to be coming from above that black part of the pipe, the dampness on the plywood also suggests that.
http://i.imgur.com/kiuQ14L.jpg

Removing the drain cover reveals this black stuff that looks to be a bit wrecked...
http://i.imgur.com/XgtzlSa.jpg
http://i.imgur.com/ZW6CilD.jpg

Seems like its some sort of sealant because its all over the underneath of the cover too:
http://i.imgur.com/If8Kek6.jpg
http://i.imgur.com/wwYInL2.jpg

Im 90% sure that black stuff being wrecked is causing the leak... question is, wat do?

 

[MaxP779]

I'd just buy a new trap and drain only a few quid. Clean it all up dry it off thoroughly and refit with some fresh silicone.

Are these things all standard sizes? What kind of silicone should I use? I read someone say to use something called "plumbers putty".