Send it to JamesDean (Kris Rose) for analysis and repair. Not only can he bench test it, but he can often fix what's wrong. The one in my SDL would set or cancel, but that was it. Would not decel and would not resume. Often after setting the speed, it would "run away" then become permanently cancelled until the power was cycled. The cruise amp was bad, likely one of the digital logic chips had failed. Both he and I poured over that board and never did find the problem. He rebuilt a core and sent it back and been working flawlessly since.
His website is here:
Overview