My hipster t400 had a real light spring in it, & I
think they said the pressure will keep it out.("pressure release") My current JW brake has a monster spring on it & has been giving me fits with the solenoid not engaging occasionally (usually 1st or 2nd rd
) I think the case is swelling under heat & making the valve stick, because when you manually push it in it starts working again.
If your 350 is like the 400 ,& I think it is, the solenoid pushes into the case where the modulator went, & is held in by a bolt & retainer strap.