The RM
exhaust system is fairly straightforward and the commonest sections to fail are
the flexible pipes.
Here is a
diagram of the standard AEC exhaust from an old Truckmaster catalogue.

The original AEC part number is shown with
the Truckmaster and Wasey equivalents. None of these three suppliers is still
in business but a good commercial vehicle exhaust supplier should be able to
cross reference from the old Truckmaster part number given above. Commercial
Vehicle Exhausts Ltd used to supply some of the sections but they have now been
taken over by Dinex Exhausts Ltd http://www.dinex.co.uk/index.asp?pID={C1E258D7-288F-4819-B636-1AF5C1A5C0B2}
The Dinex part number for the silencer is 16304. The silencer is fairy easy to fit. Make sure you
install it with the arrow on the casing facing towards the tail pipe!
Update
(May 2008)
I’ve
just bought some new exhaust sections. Dinex still seem to have good stock
levels of them
The
tailpipe (TAE22M) above is Dinex part number 16606 (£60) and the section next to it (TAE31B) is 16608 (£47.50).