Changing the ATF

Has anyone used one of the specialists that have a machine to flush out the slushbox and renew the fluid?  Any recommendations near either Ludlow or Swindon (we're moving house at some indeterminate point in the next 3 months)?

Unless you need need to the general consensus is to leave it alone. Is it brown or smells of toast?

I thought the consensus was to change it before it got bad, but not to change it once it HAS gone bad (as the crud in the fluid helps worn-out clutches get a grip - changing the fluid too late can result in a non-working box).

The car has done 53,000 miles over nearly 13 years.  The fluid is still a nice red and the box works as it should.

I'm mostly going on what I was told by my 2 local suzuki dealership service departments, whom were both being offered the job?

Also I seem to remember that service book says 90k or something.