I have a Brother Innovis 4000D. When you are sitting looking at the machine, the left most part which has the take up thread lever on the right side of it is the only part that is easy to get off. There is a small screw on the back side, and you just slide the end cap off. My service guy told me to put a drop or two of oil on the needle mechanism, same as any mechanical machine and let it sew some without any thread. Mine won't. I have to put a piece of material in there that I don't care if it gets a bit of oil on it and just sew. He did mention a drop in the bobbin area, but I forgot where. Mine ends up needing some type of attention about every two years so I let the service man do the clean and oil at that time.
I oil my very used Nolting long arm in the same way, except that it has 4 little openings at the top and I put a drop in the bobbin race, which is what the bobbin sits in.
Hope this helps.