Bosch dishwasher 1993,SG13012 GB, has started leaking on bottom left hand s?

Are you sure it is leaking from the door and does it happen on every wash cycle?
I had a very similar problem and eventually found a solution on this site. There is a steam release on the internal right hand side of the machine (grey plastic round aperture about a third of the way up if you look in the machine) if this is covered by, for example, a plastic chopping board, the machine can't vent the steam and it simply founds another way out. In my case this was as you describe from the bottom corner.

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November 2010