ssh reliability problems

[Eric S. Johansson]

tunneling X traffic over ssh seems to fail at the four to six hour mark. 
 all the connections shutdown with little reported information.  Normal 
ssh sessions stay running fine.

yes, I am using the -Y option is recommended in the FAQ.  I am using a 
reasonably current (as of last week) copy of openssh via cygwin.

ideas?
---eric