Heat in moderation wont hurt it, Ive heard stories of using punches to loosen these and i wouldnt recommend it. They will break and then you are screwed unless you can find a used one. I have yet to find a spanner wrench that will remove one. I used pipe wrenches in the past but the metal is so hard its hard to get a bite and if it does bite you have to make sure you dont get to close the resevoir account it will muck it up and it wont seal. I have a homemade tool that works rather well and essentially all it is a flat piece of steel with notches that have 1/4" flat stock to fit in the spanner grooves on both sides. It may take a little experimenting but if you have a welder i would recommend this route.
Thank you for the advice. Unfortunately I don't have a welder, so I'm going to have to do it the hard way. So, if I do mess it up in the process, do they sell a replacement "nut" for a Walker?













