The Riverstone RS platform was never intended to operate as a full-transit BGP peer due to its flow-based architecture. Because of this, there are often a very large number of short lived flows resulting in very high CPU utilisation and control plane instability (e.g. during DOS attacks).
The
link that Schumie refers to explains it in much more detail.
Since Riverstone was bought by Lucent, and the subsequent merger with Alcatel, the RS platform is now EOL and Alcatel-Lucent will only support you if you have a current maintenance contract.
I sugguest that you look to replace the RS8k with a Cisco 7200 router or, better yet, look at
Vyatta.