I just upgraded to solid aluminum body mounts and I was really surprised it made a noticable difference. Granted my original rubber ones long gone, but now the steering feels more "connected" and less body lean (probably literally).
When things get hot the tend to expand. Have you tried going for a 15 minute highway drive then coasting almost to a stop then brake? If it still clunked you could assume it's in the brakes. Otherwise it's under the hood, maybe your rag joint is close to the exhaust which allows it to eventually expand and take up some slack?
