Ok, have updated the diagram, so subject to your final check that its correct and putting in the resistor values for future reference, my job done.
So, what route are you going to use to repair it , just the triac , res, and transistor or all the active parts ?
Also , short of the proper meters, do a visual check on the 4 electrolytic caps, are they secure, any leaking substances and are the tops of the tubes flat ? if they are slightly bowing upwards thats a sign they are failing.
good luck