Do you think if you had access to a air compressor with a blow gun and used a 9 Volt battery to activate your solenoid you might have been able to blow out the trash the solenoid?
I am also wondering if people have problems with this solenoid, they might be able to blow it out while still installed on the car? 1. to save money and 2. so they do not have to remove the solenoid??
I am just taking a guess and stabbing in the dark here, but if you could connect a piece of spare vacuum hose to the solenoid input, you could use the blow gun to pressurize the engine side of the solenoid and blow backward through the solenoid and possibly dislodge any trash that may be causing the solenoid to not close correctly?
You could even use the car to active the solenoid by doing this test at first cold start as the solenoid should be active for the first 90-120 seconds. You would need to disconnect the vacuum hose at the SAP check valve.
I know attaching the hose to the engine side of the solenoid might be hard, but probably easier than removing the solenoid??
As for the small check valve (not the solenoid), I have not had one in my hand, but I know the VW/Audi check valve that look like this BMW one have problems where they crack and leak vacuum all the time as well.
Seems that the small check valve and short vacuum hoses between the solenoid and the engine connection are prime suspects as well, but no fun to get your hands on?