Synching Problems

I've filmed a live event in a theatre using two cameras. The sound was recorded
onto MiniDisc using the recorder in the theatre's sound system.

I've now got all the footage captured onto my PC, and I've recorded the audio
from MiniDisc to .wav files using Adobe Audition. I've imported everything into
Premiere and now I'm trying to sync everything but I've run into two major
problems.

Firstly, the sound recorded from MiniDisc is running at a different speed to
that captured along with the footage. I've synched it up at the beginning, but
it soon drifts out of sync. This has happened before, and I've worked around it
- I synched it at the beginning, then synched it at the end and noticed that to
do so I had to move it about 6 seconds. So I stretched the audio by 6 seconds
and it was fine. However this time, the sound is drifting out of sync very
quickly - it is noticable only a matter of minutes after synching.

Secondly, I am having the same problem with the footage from the two cameras! I
have synched it up at the beginning, but by half an hour into the video there is
a noticable lapse between the two.

      But what can I do about the second problem? What could be the cause?