Thanks for the help sir, I'm going to regroup and try again soon. If I understand correctly it sounds like the pipe covers as much of the spanner as it can. The pipe I used as a breaker bar only went halfway up the spanner, which caused a weak point. If I purchase the same style spanner again i'll go with a larger diameter pipe.
That might be all it takes if you can choke up on the spanner close to the cap and have enough length of pipe for leverage, it will let go with enough grunt (and cursing, that does help). You could try to get some penetrating oil on the threads as well, with some time it might find its way in there...
Thanks for the info sir! I think maybe i'll try that Ampro wrench next, though i'l have to buy the 1/2" breaker bar too I guess. I don't want to risk breaking my 1/2" drive wrench on it.
No problem! The Ampro I found is one of a few knockoffs of OTC (best quality but expensive), if you go that route yes definitely invest in a 1/2" breaker bar, ideally one with a good lifetime warranty