Not sure what to order - no 4 digit code

Thanks for your patience during this busy season. I agree this looks like an S385-21 to me. The only other possibility is the S380-21; this is identical except the bottom nylon fitting has a depth of 1", rather than the 1-3/32" depth of the Series 385. Take a look at both if you haven't already to confirm the best match. 

You might also want to make sure your Top Sash Guides are intact. See the video below.