Debris in radiator hoses, ULS 5-year rubber

[RandomSquawk]

I'm going to call Vans Monday, but until then I'm hoping for a little education from the VAF brain trust. While replacing the cooling system hoses on a ULS (600 hours, 6 years) I found these gems (see photos). The large radiator hoses had plenty of crud easily rubbed off the inner walls. The springs within them (part FF-1208C) had substantial crud buildup on the mating surfaces, and it does not come off easily. At least the crud is not circulating (drained coolant was fairly clean). Note the small hoses did not have any crud on the inner surface.

1. How common is this crud buildup, and what causes it? Vibration against the spring? Poor choice of coolant? Just old rubber?
2. Should I be concerned with this amount?
3. When switching to silicone hoses, is this spring advisable at all? I'm planning to use Flexfab 5521, per some other posts.

Thank you.

 

[SPRV12]

You will need the spring to make the same sharp bend without crimping the hose. This black is due to deterioration, which is why the rubber needs to be replaced. Silicone will not have this issue.

 

[RandomSquawk]

You will need the spring to make the same sharp bend without crimping the hose. This black is due to deterioration, which is why the rubber needs to be replaced. Silicone will not have this issue.

It's curious that the vast majority occurred right where the spring contacts the hose. Silicone may not age (as fast), but will it "wear" on those contact points?