I bought mine last in 1982 NOS GM on the shelf at Bristol's Chevrolet.
Classic HQ is making a reliable replacement that has a 1 year warranty and come pretested. Uses new tooling, and quality steel. $84.95 http://secure.classichq.com/68-69-RS-HEADLAMP-VACUUM-ACTUATOR--P485C59.aspx
Rick's also selling these new tooling versions from Classic HQ but cheaper at $79.99. http://www.rickscamaros.com/camaro-headlight-door-vacuum-actuator-rally-sport-rs-1968-1969.html
Classic Industries sells a different tooling replacement manufactured by/for OER - no warranty, $79.99. And we all have our opinions of the quality of any OER product.
But a fresh set of hoses, good vacuum from your intake manifold, new or rebuilt hose bib on the headlight switch, lubed bell-cranks, and silicone lubed canisters, and PJ on the pistons and sealed dust boots make the doors as quick, and reliable as a vacuum system can be.
I love the mechanical pace of the doors on a 68 or 69 vacuum system. I find the electric conversion units too quick, and way too loud to fit the late 60's vibe of the car's design.
As to the binding situation I would check the piston connection and make sue the clip its making contact with anything, could the hose have gotten in the way? Basically look at everything you took off and put back on.