Parked the car up over night after being used, next morning removed all the spark plugs and placed some old blankets around the engine bay and front wings. I then got someone to start the engine whilst I observed .... which resulted in water being pushed out of the spark plug holder of cylinder number 5 only.How have you identified that you are getting water/coolant into cylinder 5?
Once no more water was being ejected, sprayed some WD40 into the cylinders, put plugs back and started engine which of course ran much better much quicker on cold as I guess no more water in the cylinder being pushed out to through the manifold.
To be honest I am only going to know for sure once it is all apart and I will get the head pressure tested beforehand.
Kev