Intermittant resolving issue

[GeekGrrl]

I am experiencing an intermittant issue resolving a hostname on two of my
nameservers. The other six resolve correctly, all of the time. This is
what happens:

The host I am trying to resolve has a 60 second TTL. It is
delegated out of it's parent domain by NS records to another set of
nameservers. My other 6 nameservers, including the primary and secondary
nameservers for the parent domain all resolve the name all the time. Three
are external caching servers, two are the authoritative servers, and one
is an internal lan nameserver which can reach the outside world, but the
outside world cannot get in to. The two servers that are having the issue
are a caching server on the outside world and another internal lan
nameserver on the inside world which can get out, but outside cannot get
in. 

Since I can get good answers consistantly on 6 servers, I assume that the
gtei.net servers are serving up correct, timely and accurate answers. What
I need to know is why the two servers get intermittant 'Servfail' on this
hostname and how to fix it. What should I be looking for in /var/adm?

The guilty LAN nameserver is running BIND 8.1.x (yes, I do have
upgrading planned) and the guilty caching server is running BIND 8.2.2P5.