Yes, I am a member of that club too. To do some FMQ, I couldn't get the tension right. After cranking the upper tension to the max 9, and this machine is NOT the kind you can take the bobbin case out and turn the tiny screw. So what to do? In the bobbin area there was a 1/8" diameter flat button with a + an - and a line in between. Huh? what's that?

Out came the 40 yr old manual, and what do you know....it's a tension adjuster, and that black line is a painted screwdriver slot! Who knew?

BTW, my FMQ just improved today! You are not alone..... ( I bought this machine new 40 years ago)

It miraculously improved, how awesome, lol. Glad to see my club has so many august members. :D