The Allure is a very nice coach.
Some things to check/investigate:
1. PTO mounted to transmission that runs the power steering and the hydraulic fan motor is a known problem if it is the 'dry' PTO that originally was installed on the coach. There is a 'Wet PTO' upgrade kit that may have been installed but I would have someone verify. Info at CHELSEA PTO
2. Inspect the tops of the slide rooms to make sure the sealant is still in good shape. Also check the small metal angle trim pieces at the top and bottom edges of the slide rooms. Both of these areas were potential sources of water leaks. The small angle pieces on the corners were attached with a sealant and, if loose, need to be resealed and attached with fasteners. I removed mine (they were loose, sealed them well with caulk, and reattached them with rivets.
3. Country Coach, along with Monaco and perhaps some others, used radiators from about 2003 to mid 2007 that were known to fail and leak. Not all leaked but many did and had to be replaced. I have one of the suspect radiators but it is holding up at 8 years and 52,000 miles. You can call Country Coach in Oregon, give them the coach serial # and they can tell you if the coach had one of those radiators when it was built. It may have already been replaced during warranty or by a previous owner.
FYI, Country Coach has reopened in Junction City, OR and does offer parts, tech support and service. Another great source is a former CC tech name Kevin Waite who owns and operates a service business in Junction City. Kevin is another great source for info, parts and repairs if needed. His number is 541-953-6162.
My other advice is, depending on where he bought it and what service he can absolutely verify it has had, I would take it to a competent commercial truck shop (Coach Care, CAT facility, etc.) and have the chassis inspected and have all critical service done to include oil, filter, air dryer serviced, rear differential lube change, chassis lube, hydraulic reservoir filters, engine air filter, service generator. Also, if a 2004 has the original engine coolant, it time to do a cooling system drain, flush and refill with new coolant. OAT long life coolant, like Final Charge, is highly recommended since it will last many years.
At 11 years, I would change any engine belts and perhaps the main coolant hoses. If the coach has the Hydro Hot or Aqua Hot heating system, that should be serviced if there is no evidence that has been done. Annual service for those include a new fuel filter, cleaning the combustion chamber of collected soot, and installing a new fuel nozzle.