Unfortunately it is a common problem. They can repaired - see dorsey's pinned topic in this section and the newsletter. Otherwise, you have to buy a new light bar, either Juwel or an Arcadia I bar. The Arcadia ones are only made for T5s now, but Juwel still made T8 ones last year when I replaced mine. It was a month out of guarantee!
Edit - just noticed you said Highlites in the title. Must learn to pay more attention. Those are the T5 units aren't they? I thought they were supposed to be more reliable. The shop where I got my new T8 unit from said the T8 ones were made in China, while the T5 ones were made in Germany, with German engineering. That was supposed to have solved the problem. Are you sure the ones on ebay had the newer T5 light units?