| Simon, they are pretty bomb proof. Unless there made from cheese metal or machined incorrectly, they should be OK. It's the plates and the basket that wears out and need more frequent replacing than the non slipper type. I would check to see if the basked is unique or if you can use other makes when it comes to replacing it. I highly recommend using clutch plates with the thicker aluminium tabs, such as the ST4S plates (I believe). Don't use plates with steel tabs as it will knacker the basket in no time. Don't know which kind the surflex are but the ST4S plate sets are not that expensive.
Other than that, you'll need to grease the ramps and balls frequently with hi temp grease. I assume this has balls and ramps, not just ramps. | 
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