Hi Ian, sorry to hear about the problems you have had with your C5, you must have been very unlucky with this car, I am on my 4th C5 estate, I also have the new model on a 58 plate, I have covered 43700 miles and I also tow with it, it has been very reliable and tows very well.
The previous 3 C5's were company cars which I also towed with, these were relaced every 30 months with an average mileage of between 125000 to 132000 and I never has one single problem with any of them, they were on the original clutches when they were replaced.