Older Warwicks had an alluminium truss rod to keep the balance good...
But these rods aren't very tough. You should replace it with the steel version. A bit heavier but much better. Yes, the truss rod on your bass can be replaced without removing the fingerboard. But I'd suggest to have it done by a repair man.
Contact Warwick to see if they can send you the truss-rod. Or, if they don't help you, drop me a line and I'll try to help (I have a line to a shop that carries Warwick replacement parts).
