Even if the membrane is shot you can maybe fix the board by getting a spare one instead of an entire keyboard... I fixed my 1200's this way though the chap who sold it had packaged it very badly (it was creased and crumpled up from being folded up inside a flimsy thin box with no protection - the box arrived basically destroyed) but despite that it worked!
look for amiga 500 'membrane' or 'membraine' or something on ebay, he always seems to have ridiculous typos in his item listings.
