I have a different opinion about K-Seal to most people on here. I had a car which was leaking water from the head gasket, no oil loss or cross contamination. I had intended to try the K-Seal as a temporary remedy but I ended up running that car with the K-Seal in for 3 years. The head gasket did eventually go properly, a week before my MOT was due
, so I replaced it.
So I would say that as long as you only see the K-Seal as a short term solution, to get you over Christmas for example, then shove it in. But only if it is water loss that is your problem, if you have water getting into your oil or vice versa then don't use it.
But you have to be prepared to do the head gasket job sooner or later.
Also, once it's in you will not be able to disguise the fact that it is in there if you want to sell the car. It will be spotted by even the most careless buyer as the filler bottle will be full of bright copper particles and they will either run a mile or seriously knock you down in price.
Ian.