Overview
The Taurus SHO, like any car (and any (mostly) American car, in particular), has a great many parts that are known to fail. Some of these are regular wear items (eg, spark plugs), some are common failures at the middlin' age of 100k miles (eg, water pump), and some are very infrequent-but-deadly items that should be checked (eg, thermostat->catalytic converter failure). The division into these categories is somewhat arbitrary. Generally, the "wear items" ought always to be changed at some interval, the "usual failures" are effectively wear items (consider yourself lucky if you don't have to deal with them), and the "Rare but known" are mentioned because of seriousness if they do happen.
I realize that this list could become arbitrarily lengthly, until it encompasses every dang part in the vehicle. That's not the goal.
This list attempts to be comprehensive for the GenI/II. If you have any suggestions, please send them to the author, Alex Winbow.
(However, until this list has been thoroughly vetted by owners of long experience, it should be regarded as a bunch of hearsay by someone who only barely knows what he's talking about!)
Engine
Area
Wear items
Usual failures
Rare but known
Intake
EGR valve
butterfly valves
Exhaust
muffler, gaskets
catalytic converters
Seals
front main, rear main, pan gasket, valve gasket
Plugs, etc.
spark plugs, plug wires,
boots, plug wells (oil-filling)
Cooling Plumbing
coolant
hose-connections (metal->plastic), hoses, waterpump, thermostat
radiator
Belts
timing, a/c, accessory
Sensors oxygen, CID, CPS
VSS
Air Conditioning
evaporator, compressor, condensor, hoses
Electrical
battery
alternator
Pumps and filters
fuel filter, oil filter, air filter
fuel pump, oil pump
Structural
motor mounts
Engine proper
valve shims
cylinder walls (scoring), rings, valve guides, camshafts , crankshaft, connecting rod bearings
MTX Transaxle
Area
Wear Items
Usual Failures
Rare but Known
Clutch & co.
clutch disk
clutch plate, throwout bearing
Differential
differential pin
Other
trans fluid
synchros
Suspension, Steering, etc.
Area
Wear Items
Usual Failures
Rare but Known
Brake actuators
pads, rotors, calipers (front/rear)
Brake hydraulics
brake fluid
master cylinder, ABS computer, BOO switch
Steering hydraulics
power steering fluid
power steering pump
Front wheels
tie rods, tie rod ends, CV joints
Suspension per se
struts,
strut bearings, sway bar end links (front/rear), control arm bushings
Other
alignment, tires
Exterior/Interior
Area
Wear Items
Usual Failures
Rare but Known
Wipers
wiper blades
wiper motor, washer pump
Lamps
head, hi, fog, corner, running, brake, turn, high-brake
Moonroof
moonroof seal
moonroof console