2008 Mercury Mountaineer/V6/AWD/190000 miles/automatic.  Scan code P0401. 

Planned to clean the EGR valve.  Got the passenger side bolt and exhaust tube loose, but the driver side bolt is buried so deep that I can barely get a normal 3/8 ratchet and 10mm socket on it.  Have used several applications of PBlaster and a torch, but it is rusty and will not move at all, at least with anything I have that can reach the bolt head(they must assemble these before the engine is installed, as it's up near the firewall, plumbing, and wiring harnesses. There doesn't seem to be a way to include a photo).  We really can't afford to have a mechanic work on this right now.  What is the correct tool--rent or buy--for the job?