The early ones are. The later ones like the FBG in your 2002 seem to be more affected by the A-drum roller bearing collapsing which then causes the clutch pack to slip and shreds an o-ring which releases line pressure causing all the other clutches to also slip.
Changing the valve body is simple if you are meticulous about detail and cleanliness although its a very messy job in the car since it holds a lot of oil which will drop on you
I would argue though that if its shifting ok then changing it is a waste of money. The best preventive maintenance on it is to change the bearing, but that's inside the box behind the oil pump so is a considerably bigger job. Still, its pretty obvious when that bearing has failed (clutches slipping) and if you get to it immediately it won't do any lasting damage.
Treat it to a new MAF if you haven't already - that has a surprising impact on the gearbox behaviour and longevity
I'll ask a mod to move the thread to the D2 section for you