well i got the bolt out finally. i tried various things , oil, jamming stuff around it ,and i finally started to get it out by taking a rotary file and cutting plastic around the nut @ 1inch. i was hoping to get a vise grip on the more exposed nut/insert. i removed about 3/16 of plastic and was just trying to get on the nut . the brass nut will break away when you try to grab it hard. i then tried to heat the nut with a plastic welder[ hot air, small stream] and try to move it out futher to get a better grip. i did get a better grip and was trying to hold the nut and also turn the bolt stub .......... still would not come out!!! finally i had a good grip on the nut and still that bolt would not come out.ugggggg i heated it up again and this time the nut actually pulled out of the tank. the tank is pretty thick there @ 5/8 thick. leaving a nice square hole and no fuel coming out. the actual nut/insert is brass and about 1/2 inch long square and has channels around it. i put the insert in a vise and my big vise grip and the bolt stub finally came out.!!!! to repair the tank i cleaned out the square hole of debris[ the inside of the hole was rough] and coated the insert as well as the hole with epoxy. i left the suface low by @1/8 inch .. after the epoxy dried i then filled the rest of the hole with clear plastic from my plastax repair kit . i sanded it smooth . it looks pretty good and the hole is operational. bottom line is make sure the bolts are the right size and it probably wouldnt hurt to put a little grease or anti-seize on the bolts .