A french magazine (Moto Journal) did a 50.000 km test with a R1200GS; here are the results:
very positive report, the GS is almost new despite some well known problems (ABS faulty at 15.900 Km, replacement of the rear drive at 18.750 Km and gearbox at 37.900 Km...);
the cost price (everything including 3.000 litre of petrol) is 0,133 Euro per Km;
in 50.000 Km they had to change 2 sets of front brake pads and 4 for the rear, 2 H7 bulbs, 5 front and rear tyres, 5 oil filters, 4 spark plugs; the overall oil comsumption is 19,75 litre; the overall cost for the revisions to the dealer is 1.082,60 Euro;
they opened the engine and found that the valves were worn but no replacement was necessary; the camshaft is new as the cylinders; the clutch is OK; no rust on the bike just some very small corrosion; the compression of the engine is fine; the rear disk needs to be replaced.
After 50.000 Km the bike has lost a very little bit acceleration; the overall petrol comsumption is 6 litre/100 Km and 0,1 litre/1000 Km for the oil;
very positive report, the GS is almost new despite some well known problems (ABS faulty at 15.900 Km, replacement of the rear drive at 18.750 Km and gearbox at 37.900 Km...);
the cost price (everything including 3.000 litre of petrol) is 0,133 Euro per Km;
in 50.000 Km they had to change 2 sets of front brake pads and 4 for the rear, 2 H7 bulbs, 5 front and rear tyres, 5 oil filters, 4 spark plugs; the overall oil comsumption is 19,75 litre; the overall cost for the revisions to the dealer is 1.082,60 Euro;
they opened the engine and found that the valves were worn but no replacement was necessary; the camshaft is new as the cylinders; the clutch is OK; no rust on the bike just some very small corrosion; the compression of the engine is fine; the rear disk needs to be replaced.
After 50.000 Km the bike has lost a very little bit acceleration; the overall petrol comsumption is 6 litre/100 Km and 0,1 litre/1000 Km for the oil;

) my trade in is probably $10,000 but an HP2 will cost me another $16,000 and realistically will cost me the same hit in a few years if I do the trade in dance then.
Who's going to buy a 3 year old one with 100,000 km on it?
I wouldn't and I know the rider. But I bought it to ride not sit and look pretty so when you consider the kms involved I'm sure my pennies lost per km is far less than most. Smiles per km certainly exceeds the trade in value too. 
