Clunk noise...?

[HONES]

Well the story is when i pull a second geary or gunn it around a corner i hear a clunk noise from about under the park brake...so i jacked the car up and noticed that i was missing a bolt at the middle kinda back end of the tailshaft and one was fair loose.
So i got another bolt off my old car and tightened the other one up (all are tight as a virgin now). So i took it for a test-thrash and its still doing it. Its coming from just out of the gearbox or around there.
The noise isnt a big clunk but alot of little clunk noises like the tailshaft is banging up against something about 5 times a second (what it sounds like)

Dad seems to think a new rubber seal from the middle of the tailshaft coz he can push it up half an inch or so.

Has anyone got any ideas coz its really starting to get to me...cant even have a decent thrash.
haha
Cheers

Jones