matched quads, one dead, then what?

My search skills have failed me: if you have a comparatively new (~100hrs) on a new matched set of quads (in this case, winged C EL34's), and one of them dies...is the theory that you replace the whole set of tubes? Or do/can you send one of the functioning ones in to be tested, and have the replacement tube matched to it?

This is why I've started with an inexpensive tube amp, and affordable tubes. :-)