WC-78 coinco mech questions

[LEDCREATIONS]

So Ive been playing around with this machine and one time inserting a dime I got the machine to vend a complete cycle. I tried to do it again and nothing.
number 1 is the amount selector 5-25 cents now when I adjust it and insert a coin solonoid 2 cycles it back to 25 cents. Number 3 is where the hummming noise comes from. number 4 as far as I know hasnt done anything.
Now when I play with the empty switch and click it as its empty the humming noise stops.
My question is does anyone know what might cause this issue? What commonly breaks with these mechs and are replacement parts around for it?

[LEDCREATIONS]

Side note: free vend works