Hello Mick et al...
Good to hear your getting on top of those pesky coolant leaks at last

Two Points...
1) the water pump.
The short answer is it can be rebuilt, the trick(s) are getting the correct parts...they are all out there, it's just a matter of perserverance in tracking them down, through places like Bursens, CBC, Repco etc. OK, trick one is most important. Before pressing off any of the components, is U preciseley measure distances of each of the components as they sit on the assembled impellor shaft.
The reason why Honda do not supply individual parts is because the assembled pumps are
jigged prior to assembly. This is because it is critical for the seal preload pressure and both its position on the shaft and that of the bearing is essential to providing both a water-tight seal and ensuring the load bearing is in a nuetral position as possible as the whole assemble (as U know), is driven from the outside of the timing belt on the immediate driven side of the crankshaft. You will note, if U chose to dismantle the pump, the impellor shaft doesnt have set steps or lands whereby you can simply press on each component and know its in its correct position.
Trick 2 is when pressing the parts that compose the seal assembly is to get both the correct amount of spring pressure to ensure a water tight seal AND the remaining shaft is its correct position so that the bearing, once pressed on WITHOUT altering the work you have already done isnt messed up and the bearing is on the shaft in its correct position. Really, without a jig, the entire assembly is in the skill and feel of the person undertaking the task. So, the meassurements U take before and during dismantling the pump, become just guides for reassembly as the replacement parts will, in all liklihood be dimentional a little different.
So, the short answer is it can be done but it is technically challenging.
2) Timing belts.
The most important kilometer post is 100,000km and not 150,000km. At 100k the timing cover(s) should removed, the belt inspected (need not be removed), AND re-tensioned as per the OEM maintenance guide, which is on this web site. IF!, you tow a trailer or routinely ride hard and load heavy, I would reccommend U bring fwd this inspection to between 60-90k's.
What happens the fabric cords imbedded within the belt begin to fracture and break. Keeping the correct belt preload will reduce this, it will not prevent it.
I cut 5 timing belts in half to try an show people this, but was unsuccessful as the elasticity of the rubber held each belt to its standard length. But trust me, all ST1100 timing belts will fail, given enough time.
AJ, my neighbour is presently stripping down an 1100 for another project. It has a broken timing belt just where I expected it would fail...so when he gets the engine out, I will dismantle it step by step and I will show you just how much internal damage a snapped belt on these engines can do.
Now to pair the timing belt to the water pump. The more flailing an ill maintained / tensioned timing belt is under...the greater the likelihood this will be in shorting water pumps life as well.
Just a thought (pretty much all I can do at present),
Ciao the can:-)