Paint? Mmmm I have a mate whose 15my GSA's rear subframe paint has worn through to the metal and the metal was so polished by the leg of his jeans that it looked like aluminium. He also has corrosion to his front subframe and engine
What struck me is that in the area where the paint was worn through there were no signs whatsoever of any grey primer. It's as if BMW hadn't primed the frame before spraying it in a whisper thin coat of paint. He also has corrosion spots underneath the paint of the frame on both lower engine mounts. Note I said underneath the paint. When you look at it there is definitely a blue/purple colouring coming through the metal so much so you can feel the rust underneath the paint with your fingers. And all this from a bike that has only done 5500 miles and been ACF50'd from day one
On a positive note BMW have stood up to the plate and with a small amount of negotiation are getting him on to a 16my GSA
I have 14my GSA that is also showing signs of corrosion to the trailing edge of the offside cylinder barrel so I'm assuming that BMW will probably want to change my engine? Time will tell
An analogy that springs to mind is this:
We have a Brabantia bin in our kitchen. It's the 40 litre stainless steel jobbie. It cost about £80 when we bought it 5 years ago. It was considerably more expensive then any other bin in the shop outside of the Brabantia range. I consoled myself in the fact that Brabantia has an excellent reputation and a 10 year warranty. Quite why you would need a 10 year warranty on a kitchen bin was beyond me that is until in year two the lid on the bin failed so I ordered another lid which dually arrived.
18 months later the new bin lid failed so another replacement was supplied FOC. I noticed a link on their website which allowed me to leave feedback about my lid supplying experience so I did and on reading through other customers experiences realised that these bin lids are failing for a past time and all that Brabantia do is replace the lid FOC for the 10 year warranty period of the bin. Nobody it seems takes responsibility for the failures or asks the design team to go back to the drawing board and redesign the lid to prevent it failing in the first place
So far we have had three replacement bin lids during of 6 year ownership period and guess what? Yes that's right. the third replacement lid failed earlier this week so I am now awaiting my fourth replacement. The cost of these lids to me so far had been £Zero. Brabantia charge £40 for them if you buy them as a replacement part plus they then have to post them from Belgium. How many more lids will fail over the next four years is a guess but going by current trends I am expecting a further two at least
My mate is happy with the way that BMW have handled his problem but he wishes that he wasn't having to go through this type of episode every few years. Did I forget to mention that his corroded 15my GSA was a replacement for his corroded 13my GS ?
Now if only BMW had a 10 year warranty like Brabantia
and as the first owner on PCP you know pretty much what the trade in value (which is set by the manufacturer) will be as long as you stay within the BWM fold for your next bike so residuals are not too much of a worry. 
