Peugeot 406 V6 Head Gasket--Engine overheating

Hello and thank you for stopping to help . My Pug is a 1998 406 V6 estate with 88000 miles on the clock. It has been well maintained with over £2000 spent on it during the last year. Recently it has started running hot. It usually runs at about 78C but has been showing about 90C and above. My local mechanic has told me he thinks it is probably a breached gead gasket. It is a specialist job needing a main agent as the engine needs to be taken out if it turns out to be the back cylinder head involved.The cost could be over £3000.I have no symptoms usually described with a blown head gasket,ie no water in the oil or oil in the water and no steam from the exhaust or loss of coolant.The engine still runs as smooth and as quiet as ever.Obviously it is not worth spending £3000 on this car if it is the head gasket.However what troubles me also is that I am contemplating a 406 V6 coupe and I don't want the same problem. So can anyone tell me if this is a common problem with the V6 and is it likely to be the gasket or should I look for other causes.Any comments would be very appreciated.Thank you.