some times it is tough to know which way to go. for myself I would rather see the unit priced properly and another 2000 off if it goes with the bad entertainment hub, that way the other guy thinks he is getting a deal if he gets a cheaper one, or he is paying proper price if he replaces it with the right one. for you , your not out the extra money or time to do it.
if you put a cheep one in and list it, even if the price reflects that, you may get that guy that would have bought it if it had the proper one. trust me a lot know what should be in their because like me if they are going to look at something, they have done the research and know what they like and don't like already and where to look for common issues. if its joe off the street and just sees it driving by you could get Luckey that way.
then the third option in this economy with the price of used rv's rapidly taking a nose dive is it worth it to you to spend that extra 2000 bucks and possibly not recoup it?
what I would do, is show it as is with the price reflecting the dead entertainment center, then let them know how much it is to fix it properly and where, and have another option for them. say find a 500 buck replacement and present that as an option they could do to save a bit of money, but they might be missing this feature and that feature. have a list of the differences and let them decide. if they think its to much of a job to handle, then you could have the option of having it done after they put a non refundable deposit down for the price of the work.. that way if they back out you are not out the money for the replacement.