I visited Aero Caribbean in Havana in the mid 80s and spoke at length with the people there. By then, the Cubana Britannias were parked up and Aero Caribbean had just one in operation, flying meat from Canada. They seemed comfortable with them, but the biggest problem they had was with the big checks, for which they were flown to Monarch at Luton. I was never aware of an incident with CSA's aircraft though.
I've done four and a half hours in an IL-18 from Moscow to Ashkhabad (as it was known then). That was quite long enough!