Hey, this unanswered thread popped up on the first page when I Google searched "Type2.com", so I figured I'd register and answer it

I posed the same question over on thesamba.com a little while back, and this is the response I got:

The 018 was superceded by the 020, so if you were to go into a VW dealer and order a AFM(airflow meter)for your '76 or '77 they would sell you a 020(if they were still available today).

So you're ok. They are the exact same part, the different #'s just tell you how old they are. The door/flap in mine was sticking too, so I sanded the housing a little to free it up, since; when I popped the plastic top off the AFM, the electrical components inside looked new, therefore I wanted to get some more miles out of it.