I have an old Lauda thermostatic water bath (from 1978 or so) that 
worked fine but suddenly lost temperature control (no cooling).  The 
relay appears to have failed.  I have removed it and have googled up and 
down but the RHL 401-03, 6V 1004 24V does not seem to be available at 
all.  A picture is attached.  Its dimensions are 36x30.5x15.5 mm   Does 
anyone have any idea as to whether there might be a source for older 
relays, or whether there is a suitable substitute?  Many thanks.