VNC servers growing stale, slow

[Stephen Fromm]

We connect to a Solaris 5.9 box from MS Windows machines via VNC.  VNC 
servers on Solaris box are realvnc v. 4.0; VNC viewers are various versions, 
mostly 4.0 and 4.2 though.

I've used VNC for years, and occasionally a bug will be manifest whereby if 
a server has been running for long enough (usually months, perhaps weeks), 
it gets "stale" and is very slow, or even frozen.  I've never looked into it 
enough to know why this happens, to what extent it's an identified bug in 
VNC (versus something in X, etc).

Now, however, even fairly newly created servers are getting stale.  There 
doesn't seem to be much rhyme or reason whether a server goes stale or not; 
some don't seem to, others do.

My guess is that this isn't a VNC bug, but a problem with the Solaris box 
(probably software), though for all I know it could be a network problem.

How do I go about troubleshooting this?  (I peeked in some of the VNC server 
logs and didn't see anything of interest.)

TIA,

S