I'm glad to read you got in touch with VStech with regards to his axle booting service.
I had assumed from your thread on BW (
Homokinetic or annular? - Mercedes-Benz Forum) that you knew that the axles were at fault.
Rear end clunking is often a result of a dodgy axle however there are other things to consider such as
(off the top of my head and in no particulaer order)
1) anti-roll bar links - often made from plastic and they can snap
2) broken / rusted through trailing arms
3) stuck / sticking rear brakes / parking brakes
4) forgein objects clanking about that shouldn't be there! (road kill?)
5) problems with SLS if fitted - passenger side on a LHD vehicle is where the leveling valve sits
6) loose wheel bearings
7) loose shock absorber
8) broken spring (not all that likely on the back of a W123)
9) excessive play in the differential
10) loose wheel nuts
11) loose exhaust
12) worn bushings in the trailing arms
13) worn UJ in propshaft
14) excessive play in gearbox / transmission - in particular output yoke nuts have been known to come off
15) worn propshaft centre bearing
...can anyone else think of another?
There must be more!