On Sun, 16 Dec 2012 03:38:20 -0800 (PST), wrote:

Surely a new RCD would be cheaper.

I'm going to replace the RCD anyway. I wanted a tester to see the
difference between the old one and the new one; not to determine
whether to replace or not.

But, from the responses received, it looks like my leakage resistor
method is a fair test, so I'll probably continue with that.