Denon dnt-620 won't read discs
 

Denon dnt-620 won't read discs or will start to load up then stop. It
seems that the tray is not closing all the way. I've cleaned the tray
assembly, and this will sometimes fix the problem, but not for very
long. It will work for a day or two then same thing all over again.
Short of replacing the entire tray assembly, what can I do? There are
no error codes given when I run the diagnostic routines, except for
"disc not loaded in time"

Any ideas?