I have a 1950 Emil J Paidar model 570. You change the oil buy taking off the seat cushion. Simply lift the cushion from the front edge and it will come off. There is a lid over a fill hole in the middle of the plate that the cushion covered. Open that lid by sliding to the right or left. Fill this chair with chair with Hydraulic jack oil that you can get at any auto parts store. It will take under a quart. Not much needed to get the chair working properly.

If the chair is very old and you are going to do some restoration, you might as well take it apart and clean all the old oil out and start fresh.

Hope this helps.