I did a quick search and it appears that the 6233 is electronic. For the mid 80's that would make sense. It may not have an onboard computer, but it most likely has some electronic components which is probably why they don't want you to oil it. It may also have self lubricating metals used in it. I'm not sure how long those have been around and used in sewing machines. Bottom line, I would take it in to be serviced rather than trying to do it yourself. JMO