I'm on my 4th GS, admittedly the others weren't 1200's but I've never used 10/50. The current bike is heading toward 80,000 miles having mostly run on Halfords 10/40 semi-synth apart from when it was running in. It seems to have led a happy life on it with no obvious engine wear related problems.
The question ought to be why is there a new spec' and what's different, not where can I buy it as it may simply be BMW are making life easier by suggesting a "one oil fits all" approach to cover climate zones from scandinavia to spain, wheras in realtively cool Blighty our bikes don't really need the equivelant grade to a 50wt oil at high temperatures because it's always raining. What is important are the other specifications of this latest recommended oil and how that compares with what went before.
In addition, it's not entirely clever to bung in any old oil just because it says 10/50 on the tin. It may for example have a poorer ability to protect the engine than the 'old' 20/50 if it's not up to the required spec'.
Oh dear, this is an oil thread again..
