Is your bass anything like the one in this eBay link?
http://cgi.ebay.com/1982-Fender-Prec...QQcmdZViewItem
The asking price for this one is $2,300... might be a bit high, but if so, it's worth considering how much you want to tinker with what you have. From all reports you have an amazing bass there.
I don't know enough to be sure, but seeing as these instruments haven't been in production for 25+ years, I highly doubt you'll find a direct replacement.
If you must change the preamp, I bet you'd be happy with an Aguliar, Audere, Seymour Duncan, Bartolini, and/or many others. I wonder if you can still find the schematics for the original electronics and have something designed/built to specs....?