OK been down to see an old mate who was a Honda apprentice many moons ago and is now head mechanic at the local Suzuki dealers.
I gave him my CB650 rear shock which looks in great nick and he pushed it into the concrete floor just as a bike would depress it.
His verdict "coozed bro it's coozed"!
OK so how do we tell?
If the shock bounces straight back with no hint of a slow return then it is running on the spring only, the hydrolic side of things is knackered...time for a new one.
OK I know many on here knew this already but a lot of Newbies have asked the same question and I thought i would just post it for them.
Result: I'll be emailing Parts'nmore for a set of their $116 rear shocks...happy riding folks.