I replaced mine, but they were looking a bit worn, they are a bitch to get out mind!
The theory is you drill out the rubber and remove the debris then use a chisel and mallet and cut through the outer sleeve, slowly turning them inwards, they are nearly always corroded to the hub though. I had a machine shop get them out for me in the end as I didn't want to damage the hubs, but he used this method too.
If yours look OK I would leave them alone, it's a lot of hassle, but if they are worn and you don't replace you'll regret it later for sure. I think it cost me around £40 for the new cush drive rubbers and £70 for someone to remove them.
Andy