Trying to install diffmerge_4.2.0.*.deb
it tells me .................diffmerge depends on libc6 (>= 2.15); however:

But the version of libc6:amd64 on system is 2.13-38+deb7u1.
for
Release 7.4 (wheezy) 64-bit

Can you tell me
*) which version is for 2.13.38
and
*) what is the URL to use to download older versions, please.

I am checking into this. This may take some time.

We don't have older versions posted on the website. The best option is to update the libc. If that is not an option, then email support.