68 Proportioning Valve (Disassembly)

I am posting this on a couple of spots, hopefully someone has some input.

Trying to get the piston out of 68 Proportioning Valve.

-Any 'secrets' other than trying to use air to push it out?

-If no on that, anyone that 'rebuilds' these? I have the O-ring kit for it, but I don't want to ruin the part trying to get that piston out incorrectly. I've emailed Stanger's Site, but no response yet.

Thanks for any direction.