Wow!
We might want to start a "list of BAD indys", we could start with the shop you went to first.
Telling an owner their car is not worth fixing when it had a shorted taillight? Bad indy on a galactic level!
Root cause identification is a lost art EVERYWHERE. I had a hot water heater failure around 2 yrs ago, had 4 "professional" plumbing companies send techs to fix, all 4 gave quotes between $7 to $9 grand (direct vent unit in garage, no corrosion in tank).
Was told the unit is 6 yrs old and NG.
I installed a new burner ass'y and flame sensor ($120), no issues in over 2 yrs!
The techs all reached the "replace" conclusion with NOTHING more then a pair of slip groove plyers / adjustable wrench & screwdriver during "root cause" investigation!
