Sorry so you but NO-NO-NO!!
This is a true Paillard Maestrophonic no13, and unless a break in the diaphragm, which is almost impossible under normal circumstances, because of its design, or an inclusion of dirt, or oxidation, doesn't need maintenance.
The gaskets are in perfect shape; they are flat gaskets made of a kind of gutta-percha or alike, not rubber nor any kind of tubing. They are simply flat thin hard cushions too avoid metal-metal contact.
You can examine the diaphragm for signs of break, years or oxidation, but if it is in good shape, you must reassemble it as is, procure reassemble things exactly as they were. Sometimes there gaskets are adhered to the diaphragm due to the large edge pressure exerted by the five screws. Thus, you may know that any attempt to separate the gaskets from the diaphragm can lead to a breakage on case they are agreed.
The diaphragm is a fabulous thin and delicate aluminium corrugated marvel which produces an incredible loud sound.
All this unless someone has disassembled it before.
Just clean everything from dust or whatever, very carefully, and reassemble it.
Later I'll tell you the only adjustment possible on this.
Be careful with them diaphragm center, it's a big and delicate central dome, easily spoiled if forced when assembling.
The design of this soundbox doesn't give much room to failures, except if oxidation or dirt gets inside because of bad storage conditions.
It's dynamic design lies only in the compliance of the diaphragm itself (because of its shape and material) and of the tiny rocking plate at the needlebar fulcrum. The only thing to do is to screw firmly the five screws at the back, which hold the diaphragm edge firmly pressed between the flat gaskets. This point has no possible adjustment except tightly pressed.
The other point, the flat fulcrum plate, lies in the compliance of the copper plate squeezed between two hard steel plates at the needlebar end; I've seen this edge plates sometimes screwed and sometimes bolted (non disassemble possible) together; one of them is welded to the needlebar.
The other flexible plate edge is pressed against a flat area at the soundbox front ring edge by another steel plate tightly screwed in. This joint I'm pretty sure it's intended to be assembled and also tightly screwed in. And here's where a buzzing can originate, if these screws are loose. Although in a constant tinkering with things gramophonic, I've discovered that the degree of tightness given to these two tiny screws modifies somewhat the sound.