When i first got my 1990 N/A my gears were very stiff too.
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I first tried changing the gear linkage cables, easy to change and about
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£40-50 second hand for the pair.
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However this didn't seem to cure the problem so the next time i took it for a service I asked the garage to have a look at it and the problem was just the selectors at the gear box end had seized a little, a little WD40 and now as good as new.
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i was well chuffed.
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