First of all good to see that with your complaint you attached radiographs. According to the x-ray, it does look 27 or upper left second molar does require RCT. Also note lower left third molar is also decayed till the pulp(which has blood and nerve supply for the tooth) but for this tooth I would advise extraction of lower third wisdom tooth as it's direction tell you might be having cheek bite issue from the left side in wisdom tooth area.
Next Steps
your dentist suggestion for RCT i.r.t. 27 is right, please go ahead for the treatment
also get lower left third wisdom tooth (38) get extracted as it's decayed and would spread to adjacent tooth.
Health Tips
nothing to worry. seeing your radiograph, you seem to be pretty experienced with dentistry. all the best with the treatment