HOW MANY KM/MILES DO YOU GET FROM YOU CUSH RUBBERS?

I'm too ashamed to say, should have been on my second or third set by the sound of it.

I have heard a few grumbles about the cush drive rubbers in the latest xtz.
Being new to this l didnt really know how worn, worn was. Or how much play was acceptable at the rear hub.
After seeing a video on youtube just now l am ordering two sets first thing in the morning.
I have just clocked 25k and my dealer/mechanic has not said anything about them, even though they replaced the chain and sprockets recently during a big service.

Now to the chain.
I keep checking the slack as per the owners manual and it's fine.
But gosh does it look loose. I know it has to allow for rear wheel travel but has anyone experimented with tension or been able to check it under full suspension compression?

Are there aftermarket rubbers available?
I do remember a mod for them which l will go search for now.

All useful comments and info appreciated, by me and l'm sure many others.