Hello Rod,
There are two keys to your problem that lie in lines 1 & 8 of your question - 91 mauruder and 'Private sale'.
No one should reasonably expect a 15 year old caravan to be in perfect condition. They deteriorate simply with age. If a van has been regularly serviced and kept well, there will enevitably be some screws that will loose thier grip becuase to service some appliances the fixing screws will need to be removed to gain access. This legitimate activity coupled with vibration from towing the caravan is likley to cause some applinces to work loose under normal usage.
Unlike trade or retail sales, the condition of an item subject to a private sale has to be established by the potential purchaser before the sale is completed. Caveat emptor or Buyer Beware. Private sales do not attract automatic warranty protection, and there is no requirement for gas appliances to be safe when sold privately.
Interestingly, the Gas Safety Installation and Use regulations, require all domestic and industrial gas installtion, service repair and removal to be carried out by a qualified fitter. This even covers the breaking or making of a gas pipe joint, however Touring caravans are specifically exempt from this requirement, but the Health and safety regulations still require all gas work to carried out competently.
Some insurance companies may decline liability if it is established that a non qualified person has carried out work on a gas sytem in a caravan.
There are two possible bit of information that might be helpfull if they apply to this purchase.
Firstly if you have specifically asked the vendor if everything was working, and they confirmed it, and subsequently it was found that some were not, then you may have a case, but you must be absolutely clear on what you asked and what you were told. It would help enourmously if there was an independant witness to the exchange or some written under taking. Speak to a solicter for specific advice.
And secondly - if the seller, by way of trade or profession is a caravan dealer, then they cannot make private sales of caravan equipment related to thier trade AND knowingly give false information about condition or function. a court would expect them to behave honourably just as if the sale hade been conducted through thier business.
Again seek profesional and specific advice from a soliciter.
with the benefit of hind sight it would have been wise to have a survey carried out before purchasing in the first instance.