Looks like I need to start saving as well.... 2005 SR5 4x2 130K Cyl# 6. Have not yet confirmed leaking HG, but all symptoms match what have been described here. Just started getting the P0306 after replacing an O2sensor on drivers side bank, along with the occasional rough idle accompanied by MIL showing P0306. I have since swapped the #6 coil over to # 5, no MIL since the swap... Of course, happened just two months after purchasing this used. One thing, I did a thorough job of burping the cooling system, and have since noticed I'm not overfilling the res anymore... Just drove it to Vegas and no overheating or MIL, so I am hoping (maybe more like wishing) I don't actually have the bad HG. If so, gonna have to try some liquid fix. Any thoughts on the liquid head gasket sealers? Has anyone used one with good results?