I found this thread because I just bought an 18023 a couple of days ago. I don't know what the 5th number indicates, but assume there was a sequence and someone with more knowledge might be able to tell the year it was made by that number. For example, the 3 may mean 1973 and the 4 would be 1974. They probably did not change a lot from one year to the next as long as the first 4 numbers were the same.
The manual identifies the machine only as an 1802 zig-zag. At first glance I thought I had the wrong manual because you'd assume the 158 at the beginning of the model number would be a critical part of its identity. I'm sure I have the original manual that came with my machine, and will say that the oiling spots are a little hard to make out. I just oiled in the vicinity of where the arrows point, finding the areas where parts rub or when available, using the hole. Sometimes you have to turn the handwheel a little for the holes to come into view. It would have been nice if they'd included close up pictures of each detail, but they probably assumed that the buyer would get a demo in the store. As after market purchasers more than 40 years later, we get to wing it.
The threading diagram isn't very clear, either. Although you can tell what order the guides are supposed to be, it's not immediately obvious where the thread goes into the face cover thread guide. I think I have it figured out, popping the thread in from the front into either the left or right (or both for double needles).
It definitely came with the foot control because it is mentioned in the manual, and there is no mention of a knee control, even among optional parts available at the time. The foot controller has a device that would let you hang it on the side of your cabinet to use with your knee if you wanted to.
I'm reasonably sure that all the 1802 models had the super high shank as described in the manual and as I have seen on Youtube videos of machines with various 5th numbers - although I have yet to even see an 18024.
There is no mention in the manual of oiling or greasing the motor, which is a 1.2 amp model 2139.