unless yours is showing signs of leaking I would not bother, if it is copper then you can anneal it, as for size it has a hole somewhere around 12 to 15 mm, Rick
The original Sump Plug Washer's from Nissan are or at least were a crushable type. Although made of one piece of copper they were moulded so that the plug flattened them and any irregularities in the plug or sump. Can't think of a word to describe them but I can picture them, oh and the part number was 11026 61000 which is quite sad but sadder than that the ordinary petrol engines had a smaller version and yes the part number for those were 11026 01M02. After remembering numbers like that from my past I shall now go and sit in a darkened room :doh