Also had a problem with this rigid, small bore black plastic coolant pipe. This pipe (part # PCH001360) goes from the bottom of the expansion tank to the EGR cooler at the front of the engine; the pipe also has a protective sleeve over it, likely to protect it from chaffing. I noticed leaking OAT coolant recently and then noticed that part of the sleeve had worn away on the underside and there was a tiny hole in the plastic pipe where OAT coolant under pressure was leaking (16 years of chaffing - 2003 Disco 2). The same chaffing occurs with the HP diesel pipe from the in-tank fuel pump (the four diesel fuel pipes connecting to the in-tank fuel pump are the same small bore, rigid black plastic). I recently fitted a new HP diesel pipe and wrapped it in anti-chafe tape and then put a sleeve around it for good measure - that HP diesel line has chaffed through three times in 16 years - no more, fixed properly this time!
I noticed the coolant pipe (PCH001360) can be picked up for around $60, but I decided to wrap the area around the offending tiny hole with "Rustoleum Leak Seal Tape" - will see how this goes (has worked elsewhere for me - good for liquid and gas). For extra insurance from future chaffing I applied some anti-chafe tape as well and then the protective sleeve.
I've used a fair bit of anti-chafe tape on electrical wire conduit and other lines on the Disco 2 - chaffing of fluid lines and electrical wires is clearly something you need to be aware of!
