Spray the fittings good with WD-40 and let it set for a while. After sitting hold the line with vise grips, not so tight as to bend the lines, and then try to turn the nut on the line. If you have a helper it will work better as they can help hold the filter from turning. If the line breaks all you can do is purchase an after market in line filter and put it on in place of the old filter using a good grade of fuel line to connect it to the old lines.
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have your
seat covers clean