Got my bike back today after nearly 4 weeks at the dealer.
Engine is sounding much better now and that sewing machine clickety clack has gone.
However, I have serious concerns about what happened to the bits of the coating that came off. Have they made their way into other parts of the engine and gear box? Dealer thinks the oil filter would probably pick them up, but I'm not so confident about that.
Also, the same part number rocker arms have gone back in again, and I'm not as confident as my dealer that this issue will not reoccur.
I have sent an email to BMW Motorrad UK asking for a response from the Tech department manager. I'm expecting to be told not to worry about it and if it happens again they will fix it. This approach is probably far cheaper for them than a full recall campaign.
So, to recap. BMW Motorrad know there is a problem with the early rocker arms on the F850/750 GS. BMW Motorrad will only investigate if a customer complains of a ticking noise from top of engine (which lots of less mechanically minded people probably wont pick up on). If they find damage, they will replace the arms with the same suspect parts.
They don't seem to care about any possible damage that the lost fragments of the second hardest material known to man may cause to other parts of your engine or gear box.
If you are out of warranty, only qualified good will (whatever that is) will get you out of a very expensive repair bill.