The cooling system is the Achilles Heel of the Syncro, and after two or three decades the weakest link in the chain will always let you own on the side of Big Red when you are rushing back to Birdsville after being bitten by a mulga snake.
The only problems I have had in 15 years are coolant leaks or faulty sensors. Those plastic pipes are a pain, and I found out the hard way that you have to check that the steel inserts at the end are in place before tightening the hose clamp.
Even made up some new ones. They seem to last pretty well with the recommended coolant, but rot out quickly with just water, which some uncaring owners have been known to use.
I subscribe to the mantra of replacing all the components every ten years, and my old girl is due for a cooling system overhaul again as soon as I can find a full day to do it.
Have collected most of the parts - going for SS pipes, Christmas tree and reservoir, new radiator, thermostat, belts, hoses, baffles, grommets, and heater hoses. Even have a replacement bleed rail, but will probably just carry it as a spare in case the original let's go.
The best insurance is an audible alarm for coolant loss - then if you spring a leak, you can fix it before any damage is done. A roll of 'rescue tape' and a few spare hose clamps is a must.
A couple of hose connectors can be useful if you need to bypass a failed heater core or control valve.
I carry a set of spare hoses and belts wrapped in bubble-wrap behind the cardboard panel on the tailgate.
Speaking of hose clamps, even the best worm-drive screw clamps don't seem to work as well as the original spring clamps - the screws need tightening from time to time, where as the originals expand and contract as required.
Unfortunately the sizes favoured by VW aren't readily available - and I worry that the originals might be 'losing it'. Has anyone found a source (apart from taking out a loan to but 'genuine'?)
You need a pair of hose-clamp pliers to get at some of the difficult ones. I have a couple of different types, including one on the end of a flexible cable - they make life a lot easier.
Where there is enough space, I use two clamps.
Google 'how to use radiator clamps' as it is amazing how many people do it wrong, and toast their engine.
My next purchase is a complete set of hoses. I'm tossing up between silicone and OME quality. The genuine hoses seem to last a hell of a long time except for those little suckers on the 'oil cooler' and the one behind the drivers-side cylinder head.
Has anyone used the silicone hoses?
Some people like to coat the inside of hose before connecting them, both to help the hose slip over the junction, and help it to seal.
Some use Vaseline or rubber grease as a lubricant, which makes the hose easy to remove next time.
Others use silicone sealant or various types of gasket goo or Loctite hydraulic sealant, to make a leak-proof fit that can be hard to remove at a later date.
My old mate at the Muffler and Radiator Shop just smeared a little coolant over the inside of the hose before slipping it on.