Diagnosing SSH authentication failures when you don't have access to the client
Solution 1:
You don't need a "hacked" sshd. You should be able to run sshd -ddd to put it into debug mode.
For example...
/usr/sbin/sshd -ddd -p 2222
...would listen on 2222 if you can direct client traffic to that port. If not, stop the system sshd and start a debug listener to test the client with.
With any luck, the server-side debug will help you identify the authentication problem.