G'day Emma,

Take it to a couple of exhaust places for a quote. Depending on how much is
buggered, you can get very different prices. Also depends on how short the
skirt!

If it's just a small hole (1/4") or a crack  then it can often just be
welded up which the last time I did that to my XF wagon cost me $20.00 for
welding up 3/4 of the way around the pipe, or it could be a bigger job.
Don't worry about the hole being in a hard to get at place, a good exhaust
welder can weld upside down pipes that are hidden by all sorts of under body
obstructions. They like to show off their skill and can do it blindfolded
after a two second look at it with a mirror on a stick!

If the exhaust is standard unleaded motor it will have a cast iron manifold
which very slowly rusts out but should last for at least forty years. It
connects all the six cylinders outlets together. At the bottom of it will be
a flange gasket where the main 2" pipe joins for about 1 foot (with a T
piece with a smaller pipe going back to the inlet manifold via a silencer
and a valve unit), and then on to the catalytic converter which looks like
the first muffler. If you look underneath the car you will see the pipe go
back from the converter to the front muffler which is smaller than the
second muffler and then back over the back axle and out to the rear of the
car.

The leak can often be found easily by covering the end of the exhaust with a
rag ( macho alpha males do this with their bare hands! ) and listening to
the pipe to hear where the leak is. Two people make this much easier.

The standard factory exhaust has bolt together fittings between the
converter and the front muffler, then the rear muffler and the rear pipe
where leaks can also occur. This can be cured by using a new gasket, about $
20.00 to $30.00 fitted.

If it's the rear muffler or the front muffler many places will replace the
centre section that is both parts, but they can be replaced with a bit of
pipe at about $5.00 per metre and a single free flow muffler for a similar
and often cheaper price to the factory section that will give more flow and
a bit more get up and go! Talk to the exhaust shop and have a look under the
car on the hoist with the mechanic. With a smile and a chat you can discuss
a couple of options that are reasonably priced. You do not have to keep this
section stock if you want to keep your costs down. The pipe joins they do
with clamps and the pipe bending machine instead of the factory ones are as
good and you will get a better system that will make fractionally more noise
but will not be noticed in the car.

If you have the earlier XF with the leaded motor you will not have a
catalytic converter, just a bit of pipe. The shop is not allowed to remove a
converter from an unleaded vehicle.

All pipes rust as the motor sucks in a lot of moisture both from fuel and
the air it breaths and the condensation will sit in the pipe after short
city drives to the shop. Longer drives that heat the pipe up will dry the
pipe and they don't rust so quickly. Different bits in the system will rust
at different rates and unless the lot is buggered, then only replace the
bits that need to be. It will then hold together for another year round town
and two in the country, and you'd still be doing it all again in three years
if you went the lot.

Hope this helps,
Peter