This won't directly answer your question but the Ibanez Affirma bass, made in the early 90s, is notorious for one or more of the piezos going quieter or failing. In this case, the original designer Rolf Spuler offers a service whereby you send him the saddle and he repairs/refurbishes for around £30. Point being, its clearly not a big or costly issue getting these fixed, as long as you know where to get the work done - the latter question I cannot help you with but I would call a reputable luthier like Alan Cringean of ACG Guitars (who uses piezos in his basses) or Martin Pietersen of The Bass Gallery and see what they say