Hi there Martin,
Welcome to the board ...good to have you here!!
I will echo Michael's recommendation about the LRBaggs unit: great company that I think makes excellent products IMHO, but also their direct-fit-replacement for the so-called "barn-door" preamps make replacing an old/dead preamp pretty easy and straightforward. This and the point that Baggs makes great-sounding pickup systems.
As for the guitar, itself, I assume you can play it and it is not a web-purchase, correct? A new guitar over the web at least has "some" assurances, but a used one that has issues...well, caveat emptor is the key here.
BUT, if you can play it, then assess for yourself the action, the tone, and the overall condition. You may be getting a real bargain as it is
far more difficult to sell a guitar with "issues" in any economy, let alone in these times. If all feels and sounds good, then bargain away and get a good price. No point in shying away from a quality guitar requiring an easy fix, but only if
all else checks out. Best to you and let us know how it turns out!
Edward