there is one option for repairing the crank arm thread. it is called i believe a "steiner" tool. basically it looks similar to a normal crank extractor but the first part doesn't screw in as normal as it has a coarse thread tap on it.
this means that you gradually screw in the first part of the tool and it cuts its own thread as it goes, effectively giving you an oversize thread, then you screw in the second part of the tool which is similar to a normal extractor.
the crank arm should then come off as normal.
there is one downside, if you then re use the crank arm and then have to remove it again for general maintenance you will need to use the tool again as a normal extractor won't fit, although trust me it will easy the second time!
one of my lx cranks has this thread cut in it.
i know Gary at GA cycles in southampton has this tool. you would need to find an old school shop for this job as newer shops would simply never had any need for this tool.
also if you can remove the b/b with the arm attached which is possible depending on the b/b cup you have you should then beable to remove the axle from the crank arm by clamping the b/b cup in a vice and then carefully punching the axle out facing down towards the floor.
hope that helps.
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