Thetford C250 Toilet Leak

I ordered a new 2011 model Eldiss Crusader Cyclone at the 2010 NEC Caravan Show, I took delivery late January 2011, the first outing we found we had a serious problem with the toilet, bad smells coming into the caravan, on checking and after removing the waste holding tank, which was nowhere near full, I found that the enclosure had a large amount of liguid effluent inside, this problem persisted throughout our first holiday in the new caravan which meant I had to clean it out daily.

On returning home we booked the caravan in to the dealer to have the problem looked at and put right, the dealer replaced seals and assured us it would now be ok, of we went on our next outing and low and behold we had the same problem, after this holiday back it went to the dealer who then fitted a complete new toilet system, we thought this should solve the problem but no we still have the problem. I have spoken to the dealer again his answer being " not sure what else we can do" 

Does anyone know of other people having the same or similar problems with the Thetford C250 and can anybody offer a solution.

The caravan will have to go back again to the dealer again, 80 mile round trip, I feel this caravan is not fit for purpose so anybody have any ideas as to what are my options.