I have no idea what that white nob is on the left side.
You have all the thread guides. 10-11-12 are there and threaded correctly as far as I can see.
The motor uses Singer motor lube only, not oil. The entire machine could use an oiling but if the motor needs lube it uses the Singer lube. The belt could also be too tight. That will cause them to serge sometimes. Just tight enough to not slip and no tighter.
I agree with the thorough cleaning under the needle plate. That will make a big difference in tension. Clean the top tension too.
Joe