I just finished collecting all of the parts needed to provide a rebuild kit for 1967 - 1975 GM brake pressure differential switch/valve assemblies. The kit includes new EPDM (a rubber compound that is fully compatible with brake fluid, unlike the nitrile o-rings you can get at your local parts store) o-rings and stainless steel springs. The springs were custom made using original springs for specs. I haven't been able to test the kit out on all of the different valves that were available on GM cars, but I'm very confident that it will fit - and if it doesn't, I'll work with you to make it right. The springs might be just a hair longer or shorter than the springs used in some of the GM valves that I haven't seen. The kit costs $10 plus shipping, and orders can be taken on my web site:
http://www.musclecarresearch.com/gm-pd-valve-kit-1
Payment can be made using a credit card, PayPal, check, or money order.
Complete disassembly and rebuild instructions can be found here:
http://www.musclecarresearch.com/197...-valve-autopsy
http://www.musclecarresearch.com/197...-valve-autopsy
and here:
http://www.musclecarresearch.com/gm-pd-valve-rebuild
Feel free to ask questions!