Avondale Advice

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hi members can you help please..? We have an avondale argente 550/4 2006 caravan we have for the first time this season gone to caravan and noticed that the front main window when we clossed it that it was loose to the top right hand corner this looks like
water ingress has wrotten internal strut/main support any advice to get fixed and how much roughly would it cost.? any replies would be much appreciated..thanks