Well to be honest while working for a BMC dealership we never had a lot of trouble with the Perkins V8 in Mastiffs? A few burned oil from new but modified liners cured that, and many did 100,000 miles without anything major. They were mostly in 16 tonne gross tippers though. By a strange quirk of fete the designer of the Perkins V8 became a member of the Volkswagen camping club I was a committee member of and he was a lovely chap! 
Pete.