Hi. I went to local decent car shop, gave reg number, as there are a few terms for the car,and they sold me the right one for about £10. As to the water 'problems' double,double check the water/heater pipes from front to rear heater. The steel pipe can become porous and seep water out. This manifests in low water at thermostat ect... and can affect the head gasket.
If you can jack the car upoff the drivers side front and rear wheels, so the car is resting on the passenger side front and rear wheels. Axelstand front and rear. Crawl under and run hand and have a good look. The front pipes are metal,then about 1ft of rubber, then 2 - 3ft metal(shaped), then 1ft rubber and elbows/ bends to the rear heater via the spare wheel(take spare wheel off for a good view).I have had water probs for a year now and am replacing front to rear in full rubber until warmer then making metal middle pipes out of 15mm copper pipe and using pipe bender to copy steel layout.
OR at front of car pipes put a 'loop' feedback from one to the other as a test.then check water level. This way will bypass the rear heater.
Remember if replacing pipes to do one full runat once as it it easy to crossover the pipe.(Like in a house crossing hot to cold pipes) I am taking pics tomo,Fri, so will post soon.
Steve Gx Blackpool