I'm thinking it might be a center homing.
There seems to be a bit of dried up oil on the slider of the stitch selector. You will need to clean those up and then re-oil. As far as the tension goes, if you are experienced in rebuilding tensions you won't have much trouble taking it apart and putting it back together but if you haven't ever done one you might want to pass. Whole tensions can be bought on line for less than having someone rebuild it for you. There is a set screw holding it in. So take out the set screws and pull the tension out. Then put in a new tension and set the screws. Then you will still need to adjust the top and bottom tension. BTW those are very nice machines when they are made to work. I sold the one I had and kind of had second thoughts. They are pretty high quality. It took a lot of clean up to make the one I had work smoothly. Once I got it to work I really liked the machine. That stitch selector reminds me of some of the old Bernina machines.