Sometime back I had my tech bud help me find the leak in my WW fluid system on Superblue. Whenever you’d hit the power button, it would spray a stream up into the air in the engine compartment from somewhere behind (i.e. toward the firewall) from the fluid reservoir. 
I never could locate it, b/c I couldn’t be in two places at the same time and I couldn’t find someone to hit the button while I was near the leak area. With his help, though, we finally located the leak to be a major break in the hose far down in the engine compartment behind the reservoir. At first I hoped we might be able to block it with duck tape, but then he help up a handful of the hose and OMG - it was like black wet spaghetti - totally limp and collapsed it on itself, like a wet paper drinking straw. 
No idea what could cause the hose to end up in that condition – the portion of the hose that enters the plenum box at the passenger-side end is just the opposite - completely hardened to the point it is brittle and will just break or snap off in segments upon applying any pressure to it. 
I assume though that condition is due to the high heat that builds up inside the enclosed metal plenum box (despite the vent grill on top). IIRC, the heater core is also located somewhere around same. 
Anyway, about a year or two ago - after MUCH searching online - I had ordered a length of replacement hose from one of the usual suspects (can’t remember which one). This stuff is sort of a translucent green (tinted?) color. The vendor assured me that this was the correct size hose for a face-lift 4.0 XJS. However, when my tech bud went to try to install it on the connectors, it turns out it is just a bit too small (i.d.). I’m thinking what they sold me was something for a pre-face lift MY, or possibly even another model of Jag. In any event, there is no way to make it fit. 
So, does anyone know of a source for the correct size of hose like what I need? I guess I’ll just stick the other stuff back away in a box for possible future use 
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I didn’t try hot water (no risk of damage?) … So, does it sound like it in fact is the right size, or did they send me the incorrect one? Can’t get my $$ back anyway, b/c I got it so long ago + can’t remember which Jag vendor I got it from.