I just finished assembling the parts to provide a seal kit for use in rebuilding the proportioning/rear pressure regulating valve used on 1967 - 1969 Camaros and other vehicles. Here's a link to the product page on my web site:
http://www.musclecarresearch.com/val...-gm-mopar-prop
The kit costs $12 plus shipping. That might seem high for three rubber seals, but I had to have two of them custom made and all three are made from an EPDM rubber compound that's fully compatible with all types of brake fluid.
Orders can be placed from my web site. Just add the kit to your cart and follow the checkout process. Payment can be made by credit card, PayPal, check, or money order. I'll even do local pickup for anyone in the Washington DC metro area.