I have a Lennox G12 furnace, about 20 years old, still working well except for the pilot light which has its off moments when it keeps going out. These seem to be periodic in that it will stay on for quite a time then start going out again for a few days, after which it works OK again. I have had the thermocouple replaced twice in the last three years, at $300 a time, a lot of money for a $10 part. The questions is, could I replace the thermocouple myself, it seems to be a fairly simple job compared to other jobs I have undertaken in the past 50 years or is this a job for a skilled technician.

While you are replacing the thermocouple clead the pilot orifice. If you are good with tools give it a try if not call for professional help. $300.00 for a T couple is a rip off.