I have an early M18 that came with my first kit way back. It is a 2620-20 B58A. It sees light use really. I busted the 43-56-0035 orbital slot. I'm guessing that after they built the B58A build, things changed because for all the later builds, you can buy this part separately. 43-56-2620 is the new # that includes the case halves. ~$40 for the part. My best "guess" is that the case had been upgraded to not have this happen again. Life would probably go on normally if I fixed this one, or will it and seeing as though this is a first edition- it should go away as other problems were fixed in the later versions?