Get the survey done by a Cat dealer or Cat specialist. $1000 is chump change in Diesel world. I had the 600 Hr done just last year on my Cummins 450 diamonds $3500. The boat had 400 Hr on it when I purchased it and the broker pushed me to have Cummins do a full engine survey at the sea trial he found what turned out to be $3000 of needed repairs which the owner and I worked out before the sale. The survey cost was $1500 the guy spent a full day on the boat including the sea trial he gave me a list of findings one of which was a leaking head gasket on the port engine and a leaking raw water pump on the starboard engine. It was well worth the price to find out before I bought the boat.