Cooling (Radiators especially prone to cracking more so than the expansion tank--replace both to be safe) actually, replace ALL cooling components.
Suspension (usual FCABs, shocks will be dead if they are original)
RTAB pockets (Check these for cracks)
Rear shock towers/Front shock towers (Check for cracks or mushrooming--S52 cars less prone but still check)
Oil pump nut (Like the M54, susceptible to undoing itself usually under track conditions)
Other than that, rock solid reliable car.