I haven’t had much time to work on the VW bus lately, but I am leaning toward the intake manifolds not being fastened snugly. When I removed the manifolds, it appeared the previous owner’s mechanic must have had some issues, as instead of a stud, someone had replaced it with a bolt, AND two of the studs were very loose.
After attempting to tighten ever so slightly, they came out. So, I’m locating some step studs from the standard 8mm to 10mm. I’ll drill and retap the heads to accept the 10mm size while leaving the 8mm for the intake.