I ordered the upgraded part from WCCC because my headlight doors only work when the engine is running and so does all the other vacuum stuff.
The shop manual says which line to test but had no picture of where it physically is. I can’t find it under the hood & I don’t think it’s under the air canister because the lines head away from that.
I just have to take the dash completely off to see what is going on with it at some point.
The ones that I have seen are always near the vacumme brake booster. by the firewall.
If you have an early 67 with the twin nipple tank the check valve is embedded in the storage canister. Here is a diagram.
Bad design that was recalled, the tanks always leak and the check valves fail prematurely. Most have been upgraded by now.
I thought it was much bigger. I’m waiting for the upgraded part to arrive.