gearbox fill plug

["Brian's mail" <bsmith@domain.elided>]

When I removed the speedo gear on my 82 Spider to check it out, a whole
bunch of gearbox oil leaked out.  Now I need to refill the gearbox but I
don't seem to have a tool that will remove the fill plug.  It looks like
about a 13 mm allen head.  Can anyone tell me what tool to use for this and
any suggestions as to where to find it (my local auto supply houses don't
carry allen head wrenches that large) ?
Thanks.
Brian

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