SEAT Alhambra 1.9D 149000 miles
Have ongoing problem with losing water and having to top up. Noticed now it appears as white stains from cylinder head gasket running down engine block and also possible through another gasket. Anyone used sealant product or is it a new cylinder head gasket--or tighten down cylinder head.
Engine still seems to be running ok and at normal temperature no smoke and no white creamy crud on filler cap and water still looks clean.
Any one know rough cost of replacing gasket.

I'd guess water is coming out from around another housing (thermostat or pump) and just running round the head gasket before dropping.

Wild guess but to see what is happening, let it get up to temperature with bonnet open and engine running and see if you can see exactly where water is coming from, use a cloth to try off areas etc

Blue roll is great for working out where leaks are from.

Definitely coming from one part of head gasket. Wondering if the system was getting too pressurized and it was finding weakest points. Also looks like could be water pump gasket area as well--but that could be water from the head gasket. Will try and spot with engine running.

If its over-pressuring to the point of popping gaskets then your radiator cap (or whatever they call it these days) must be stuck if you haven't seen a cloud of steam coming out.

Normally heater matrix or some hose gives way first.