1989 TR Wheel Touch UP Paint

A search reveals Glasurit F101c as the original color, but the threads all point out that color will likely not match your "weathered" wheel color and suggest if a sizeable touch-up you rather paint all four wheels (at least the two on the same side). The weathering apparently turns the wheels a yellowish silver and perhaps brake dust and other contaminants also affect color. Someone also mentions WURTH Lacquer Spray Metallic Silver, Art. No. 0892 181 - U as an exact match.

Alternatively I haven't experimented with the auto touch-up type paints at Kragen, Pep Boys etc. but I used this from my model box and it was a pretty close match (though my scratches were very small). A decent model shop will carry multiple paint brands with several silver hues that may provide a closer match. I applied Tamiya Clear over the silver to match the gloss of the wheels.
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Found this on eBay UK. Looks very interesting, I'd give it a go but he doesn't ship to the USA

http://www.ebay.co.uk/itm/Ferrari-Testarossa-Silver-Alloy-Wheels-Rim-Repair-Fix-Kit-Scuffs-Scratches-/190681957373?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2c6587c3fd#shId