Bruce and Monepit, I think you're both right. A bad shock can be detected by the Electronic Suspension Control module and will display one or more messages on the DIC.
Specifically, the ESC module periodically sends a diagnostic signal to each shock absorber and will set a DTC if one of the shocks fails. The pass/fail criteria isn't listed in the shop manual, but I would think that if enough oil leaked out from a shock it would be detected. A light film on the top of the shock reservoir is considered normal.
If the ESC outputs a DTC, two messages can appear on the DIC:
"SERVICE RIDE CONTROL" & "SHOCKS INOPERATIVE."
Depending on the failure, the ESC can disable all four shocks and limit the vehicle speed. If that happens, "MAXIMUM SPEED 129km/h (80mph)" will be displayed on the DIC.
Here's a list of all the DIC messages that can appear (on an '04.) Other models may have additional messages, so feel free to chime in and add to this list:
ABS ACTIVE<O
</O
BATTERY SAVER ACTIVE . . . . Uh huh. . . <O
</O
CHANGE OIL NOW<O
</O
CHARGE SYSTEM FAULT<O
</O
CHECK GAS CAP<O
</O
CLEAN RADAR CRUISE<O
</O
CLOSE CARGO COVER<O
</O
COOLANT OVER TEMP<O
</O
CRUISE NOT READY<O
</O
DRIVER NO. X (1 OR 2<O
</O
ENGINE HOT, STOP ENGINE<O
</O
ENGINE PROTECTION REDUCE ENGINE RPM<O
</O
HEADLAMPS SUGGESTED<O
</O
HIGH TRANS TEMP<O
</O
HIGH VOLTAGE<O
</O
HOT ENGINE–A/C OFF<O
</O
ICE POSSIBLE<O
</O
LEFT DOOR AJAR<O
</O
LOW BRAKE FLUID<O
</O
LOW COOLANT<O
</O
LOW FUEL<O
</O
LOW OIL LEVEL<O
</O
LOW OIL PRESSURE
LOW VOLTAGE<O
</O
LOW WASHER FLUID<O
</O
MAX SPEED XX MPH (XX KM/H)<O
</O
NO FOB DETECTED<O
</O
NO FOB, OFF OR RUN?<O
</O
PRESS BRAKE TO START
REDUCED ENGINE POWER
RIGHT DOOR AJAR<O
</O
SERVICE A/C<O
</O
SERVICE ABS
SERVICE ELECT SYSTEM<O
</O
SERVICE FUEL SYSTEM<O
</O
SERVICE RADAR CRUISE
SERVICE RIDE CONTROL
SERVICE TRACTION SYS
SERVICE STABILITRAK<O
</O
SERVICE TRANSMISSION<O
</O
SERVICE VEHICLE SOON<O
</O
SHIFT TO PARK<O
</O
STABILITRAK ACTIVE<O
</O
STABILITRAK READY<O
</O
STABILITRAK WARMING<O
</O
SVC TIRE MONITOR<O
</O
TOO COLD TO MOVE TOP<O
</O
TOP INOP – VALET ON<O
</O
TOP INOP OUT OF PARK<O</O
TOP MOTOR OVER TEMP
TOP NOT SECURE --My personal favorite!
TRAC SYSTEM ACTIVE<O
</O
TRAC/STABILITRAK OFF<O
</O
TRAC/STABILITRAK ON<O
</O
TRACTION SYSTEM OFF<O
</O
TRACTION SYSTEM ON<O
</O
TRUNK AJAR<O
</O
WAIT FOR STABILITRAK<O
</O
<O</O
Other DIC Messages: <O</O
<O</O
1st GEAR
2nd GEAR
3rd GEAR
4th GEAR
5th GEAR
ACCESSORY MODE ACTIVE<O</O
CHANGE OIL SOON<O</O
FOB BATTERY LOW<O</O
HIGH TIRE PRESS LF<O</O
HIGH TIRE PRESS RF
HIGH TIRE PRESS LR
HIGH TIRE PRESS RR
INTRUSION SENSOR OFF<O</O
INTRUSION SENSOR ON<O</O
KNOWN FOB<O</O
LEFT FRONT TIRE FLAT MAX SPD 55, REDUCED HNDLG<O</O
LEFT REAR TIRE FLAT MAX SPD 55, REDUCED HNDLG<O</O
LOW TIRE PRESS LF<O</O
LOW TIRE PRESS RF
LOW TIRE PRESS LR
LOW TIRE PRESS RR
MAX # FOBS LEARNED
NO FOB, OFF OR RUN?
NO FOBS DETECTED<O</O
OFF-ACC TO LEARN<O</O
READY FOR FOB #X
RIGHT FRT TIRE FLAT MAX SPD 55, REDUCED HNDLG<O</O
RIGHT REAR TIRE FLAT MAX SPD 55, REDUCED HNDLG<O</O
WAIT XX MINUTESILITRAK READY message is displayed in the DIC
DIC Messages I'd like to see:
SERVICE REQUIRED - POVERTY IMMINENT
WARRANTY EXPIRED - STAND BY
TOP FLOPPED - BOHICA
Monepit: For you, the easiest answer is almost always to replace the assembly. If it can break on your car, it will. That being said, you aren't cursed, but your car most certainly is. The good news is, while the rest of us have cars that are aging and will most certainly fail for good at some point, yours is getting younger due to the installation of newer, sometimes upgraded parts. Eventually, you might go into your garage one morning and find your car completely disassembled, all assemblies stored in boxes on shelves -with a VIN that ends in 001! (Kind of a cross between 2001 and Highlander.) And like the Highlander, at some point, there can be only ONE. I think it will be yours! You might want to consider changing your plates to: THE ONE
CC 
The load level on the door "sticker" says limit of 300LBS (we had a thread on this before) Hope you don't weight more than a hundred Lbs. 
