How does one tell front end shimy in 1996 993 is due to shocks or front steering bush

[tshih]

My wife's 993 after a DE event at Poconos Raceway developed a severe front end vibration at speeds above 60mph. I took off the wheels and had them rebalanced thinking some weights may have been lost during the event. There was no difference after a test drive with the newly rebalanced wheels. examination of the tires show normal wear (after track speeds) and some edge of tire melting of the rubber (street Kumhos).

At first I suspect the shocks need replacing since they were abused by the previous owners mounting some heavy 18" aftermarket alloys/tire combination for the 45000 miles since new.
However according to Bruce Andersen's advice in the latest Excellence tech notes whereby he mentioned that 993's have also experienced worn front steering bushings which is responsiple for the steering wheel shimy (vibration) I am noting in my wife's car. Is there an easy way to tell which if not both are the reason to remedy the problem. The problem came after the track event last weekend so any explanation should justify that development (worn shocks just fail immediately?).

I want to find the correct cause before spending too much replacing any components that are still good.

[tshih]

Also the wheels are 17" Cup wheels that are OEM for that car which has close to 49000 miles on the original suspension and tiptronic transmission with stock ride height and no track mods.

[tshih]

Also would someone please post a photo of the steering bushings from the PET along with the part # so I can go check them out? Much obliged!